Dar es Salaam - A man has been arrested in southern Tanzania on suspicion of attempting to sell his albino wife to Congolese traders, police said on Wednesday.
Rukwa regional police commander Isunto Mantage said John Joseph was about to sell his wife Janet for 3,6-million shillings (around R35 000) when caught by a police sting operation.
Mantage said the man was caught "after the police set a trap, but the two Congolese traders escaped".
The woman told the police she was not aware of her husband's plot but he confessed to having struck a deal with the Congolese.
In a spate of gruesome incidents over the past few months, albinos have been kidnapped, killed and dismembered for witch doctors who use their limbs and organs to make lucky charms.
The latest victim was a 10-year-old girl, who was murdered and mutilated late last month.
At least 27 albinos, mostly women and children, have been killed in different parts of the east African country over the past year alone.
"It is utterly stupid for some people to believe that albinos have magic powers and their parts can make them rich," Tanzanian President Jakaya Kikwete told a recent rally by the Tanzania Albino Society (TAS).
On Tuesday, two suspects appeared before a resident magistrate's court in Tanzania's central region of Singida for conspiring to kill a six-year-old albino girl.
Did a former Beverly Hills doctor use the fat he liposuctioned out of patients to fuel his car?
The odd accusation was allegedly made in lawsuits filed by former patients and unearthed by Forbes.com this week.
Unfortunately, if he was in fact fueling his car with fat, the practice was illegal, according to California state health officials.
An investigation has been launched by the California public health department into the now-closed liposuction practice of Craig Alan Bittner, who once claimed on a Web site that he created "lipodiesel" from his patients' fat and used it to power his Ford SUV and his girlfriend's Lincoln Navigator, Forbes.com.
California law apparently forbids the use of human medical waste to power vehicles.
Bittner's practice, Beverly Hills Liposculpture, closed in November.
Several former patients have filed lawsuits against the doctor, claiming he allowed his unlicensed girlfriend and an assistant to perform procedures, causing mistakes that left the patients disfigured, attorney Andrew Besser, who represents three of the former patients, told Forbes.com.
Dans le genre insolite, on peut dire que cette brève du jounrla "Le Monde" se porte là. Selon une équipe de l'école de médecine de Peoria (Etats-Unis) composée de 10 médecins et de 5 étudiants, la célèbre chanson des Bee Gees "Stayin' Alive" serait idéale pour tenir le rythme soutenu d'un massage cardiaque !
Et oui, qui l'eut cru ? En écoutant cette chanson et donc en suivant son rythme, ils ont effectué lors de massages cardiaques effectués sur des mannequins 103 compressions par minute. C'est très proche du rythme "idéal et recommandé" par l'Association américaine du coeur (à savoir 100 compressions par minute).
Bref en cas de crise cardiaque ne vous contentez pas de mettre la chanson des Bee Gees, pensez-surtout à appeler le SAMU !
voila.. le Mexique si dangereux!
on voit les images de la maison... c'est une porcherie..
on voit le bordel à la maison, les gamins qui sautent partout, l'autiste qui traine dans un coin... combien de super nany pour éduquer ?
c'est qu'est incomprehensible c'est que c'est le meme systeme social qui a encourage cela!
A Guate par exemple ce type de situation est imposible. Si tu veux faire de la fertilisation in vitro il te faut avoir les moyens pour elever les enfants.
pour les adoptions on demande des expertises psychiatriques, financières, etc... pourquoi pas pour les FIV ?
The Sears Tower in Chicago, the tallest skyscraper in the Western Hemisphere, is offering visitors a new way to push their fear of heights right over the edge.
A set of glass balconies, nicknamed "The Ledge" and suspended from the building's 103rd floor Skydeck, opened on Thursday.
The glass is three layers thick, one-and-a half inches in total, and capable of holding five tons. but it doesn't make them any less scary.
un medicament qui te protege de la radiation comme Tchernobyl!!
A MEDICATION that can protect people exposed to normally lethal doses of radiation from a nuclear or a "dirty" bomb has been developed, reports say.
In tests involving 650 monkeys exposed to radiation equivalent to that recorded during the Chernobyl nuclear reactor disaster in 1986, 70 per cent died while the rest suffered serious maladies, the newspaper Yediot Achronot said yesterday.
Of the group given anti-radiation shots, almost all survived and had no side effects. A test on humans not exposed to radiation showed none suffered side effects from the medication.
The medication was developed by Andrei Gudkov, chief scientific officer at Cleveland BioLabs in the US. Also involved was Israel's Elena Feinstein.
(CNN) -- Afraid that her husband will leave her for a younger woman, a 107-year-old Malaysian woman is looking to marry again -- for the 23rd time.
Wok Kundor: "I am an aged woman. I don't have the body nor am I a young woman who can attract anyone."
Wok Kundor has been happily married for four years to her husband, a man 70 years her junior.
But since he left their village in northern Terengganu state for a drug rehabilitation program in the capital, Kuala Lumpur, Wok has had a gnawing feeling.
"She said that she has been feeling insecure lately and she needs to find out whether he still loves her or not," said R.S.N. Murali, a reporter for The Star. The English-language Malaysian daily was among several local media outlets reporting on the lifelong romantic.
"She is worried he might not come back after his program and find himself a younger wife," Murali said.
If so, Wok has her eyes set on a 50-year-old man, but hopes it does not come to that.
"I realize that I am an aged woman. I don't have the body nor am I a young woman who can attract anyone," she told the newspaper.
"My intention to remarry is to fill my forlornness," particularly during the Muslim month of fasting, Ramadan, she said.
Malaysian media, which has previously reported on the woman, said Wok has been married 22 times. That would make her marriages last an average of four years.
Wok would not discuss past relationships, Murali said.
"Some of her better halves have passed away or have divorced, but she doesn't want to talk about them or her children," he said.
Wok and her current husband, Mohammed Boor Che Musa, hail from the same village and met there.
Muhammad, 37, was quoted in an earlier report as saying the couple fell for each other because it was "God's will."
On Monday, he told The Star that he is still very much in love with his wife and cannot dream of life with someone else.
But Wok wants to hear him say it, Murali said.
il y en a trop de centrales en Suisse?
de ce cote ca fait envie de demenager a l'Amerique Latine!
et si cela etait vrai.. pourquoi on n'a pas donne plein de iode aux gens qui travaillaient a Tchernobyl?!
non mais.. je n'y crois pas!
j'espere que bientot on va changer tout ca car je deteste l'idee de la nucleaire... Mais bon, je viens d'un pays ou cela n'existe pas donc je n'avais meme pas y pensé!
argh!! argh!! argh!!! vous avez donc votre quota d'hypocrisie Francaise alors!


Hyperpigmentation has to be one of the most annoying skin care issues of them all. Discoloration can appear anywhere and be the result of chaffing or even genetics, and it can be extremely difficult to treat. Exfoliating doesn't always work, and for many, face creams and skin bleaches just aren't an option as they can be dangerous or make an issue even worse.
Underarms are a common area for discoloration. With underarm skin being so sensitive and the area being so close to lymph nodes, hyperpigmentation sufferers have to proceed with caution. Even if you're not into DIYs, it's a good idea to try them before going HAM on underarm darkness.
Vlogger Khloe Dosh used a mixture of turmeric, cayenne pepper, grits, and Elmer's glue to brighten her underarms and the results looked pretty damn good.
Khloe broke down the benefits of these ingredients in an Instagram post. She explained oats exfoliate and remove excess oil and bacteria, while turmeric evens skin tone, cayenne pepper improves skin's texture, and the glue helps to peel off the mask. Not into using glue? Khloe suggests mixing in a peel-off mask instead.
After allowing the mask to dry, Khloe peels off the mask then wipes away any leftover pieces with a towel.
Here's a before shot of her underarm skin.
The results aren't permanent, though. Khloe recommends doing the mask a few times a week.
Already her video has been watched over 3 million times, so if you can't find glue on the shelves of your local store, this may be the reason why.


Sleek interiors, friendly staff and great food - Dusty's Dubai has my vote!
Walking into Dusty's we felt like we walked into the set of Suits, of course you know Suits right! If you don't first OMG! and immediately go and watch the pilot episode, after reading this post ofcourse!
Everyone in formal attire (ofcourse we were in DIFC), dim lights and soothing music - ambiance was a 10 on 10.
We were here for breakfast and so our order was fairly simple - a salmon cream cheese bagel and a Dusty's Business breakfast.
Both were fantastic dishes, although we wished there was a bit more cream cheese to the bagel, but J loved the side salad.
For me the business breakfast was a 10 on 10 - I opted for beef bacon for my eggs benedict instead of the salmon, but I can't stress enough how perfect my hollandaise sauce was!
To end we decided to try out the french toast which a few other bloggers have been raving about - and it was delicious! Moist and fluffy - perfect with a scoop of vanilla ice-cream.
Dusty's definitely has my vote and with an almost 4 out of 5 rating on Zomato I feel the rest of Dubai agrees with me!
I'm sure the Happy Hour from 5 to 8 is a hit too with the tired bankers - has anyone been? Do let me know.


text:
WATCH: Josh Primo Inks Rookie Deal with Spurs
Mason Woods
Mason Woods Published: August 12, 2021
Photo Courtesy of @Spurs on Twitter
Former Crimson Tide guard and 12th overall pick in the 2021 NBA Draft, Josh Primo, is officially a San Antonio Spur. The 6-foot-6 wing from Toronto, Canada signed his rookie deal this week, becoming the youngest player in the NBA at just 18 years old.
While the official terms of Primo's contract have yet to be revealed, the rookie is expected to earn somewhere in the neighborhood of $4 million in his first year.
Joining the Crimson Tide in 2020 after reclassifying in his junior year of high school, Primo was a four-star prospect and instantly became an impact player, becoming a starter by just the eighth game of the year.
Displaying traits of great athleticism and versatility paired with adept defensive awareness, the lengthy wing showed draft scouts more than enough in his one season. Despite putting up relatively mundane numbers of 8.1 points, 3.4 rebounds and just under one assist per game, Primo's shooting percentages and potential are what solidified him as a lottery selection.
Knocking down 43.1% of his shots as well as 38% of his three-pointers in his one season, Primo also performed extremely well at the NBA combine, further leading to his high selection.
With the NBA Summer League in full swing, the fresh-faced rookie got a chance to showcase his talent in the first few of the Spurs' contests, averaging 12 points, two rebounds and 2.3 assists on 35.3% shooting through three games. In his first ever performance in an NBA uniform, Primo went for 17 points on 40% shooting, adding three assists and two blocks.
With start of the NBA season planning to be mid-October, Primo has a few months to adjust to the new speed of the game and prepare for a season in which he will likely see a good amount of playing time. The Spurs are coming off a tough year in which they finished 10th in the Western conference and were bounced in the first game of the Play-In tournament and are looking to return to the playoffs.
After trading away their star DeMar DeRozan in return for future picks and role players as well as signing Doug McDermott and the NBL MVP, Jock Landale, out of Australia this offseason, 2021 is shaping up to be an interesting year for San Antonio. Luckily for Spurs fans, Primo is young and has time to stick around for the future.
Filed Under: Alabama Basketball, Crimson Tide Sports, Josh Primo, NBA, NBA Draft, NBA Summer League, San Antonio Spurs, Western Conference
Categories: Alabama, Alabama Men's Basketball, Alabama Sports, College Basketball, NBA, Sports

redpajama_set_name: RedPajamaCommonCrawl


A last-minute bill from the governor shouldn't derail a process that involved hours of meeting between many stakeholders, and which produced a thoughtful proposal.
For months, a legislative committee, along with caregivers, advocacy groups, public health experts, law enforcement and others, did the hard work of turning Maine's vote to legalize marijuana into a bill that considers all their points of view.
The bill, which will be reviewed by the Legislature starting Monday, balances those sometimes conflicting views. It sets up a regulatory framework that prioritizes Maine business owners, provides significant tax revenue while curtailing the black market, protects children, and gives police the tools they need to contend with marijuana as a legal drug.
It's not perfect, but no legislation this size could possibly be. It's likely we don't even know where it will fall short, but even that is predicted, with a commission set up to continuously analyze the law's effects and suggest adjustments.
The thoughtful, comprehensive bill is what the committee was set up to produce, what it spent hours upon hours working toward. The Legislature should honor that with approval, so that Maine can get on with regulating — and collecting tax revenue from — a large industry that remains in the shadows.
The bill's future, however, became a lot more clouded with the announcement last week of a competing measure from Gov. Paul LePage and Ken Fredette, the House Republican leader. The governor's bill would extend a moratorium on retail sales of marijuana until Jan. 1, 2019, with the purported goal of giving the Legislature more time to work through complicated legislation.
But don't be fooled — this is nothing more than an attempt to subvert the will of the voters and stop an initiative the governor disagrees with.
LePage has played no role in putting together the committee's bill; in fact, he has actively tried to scuttle it.
Despite the committee's many attempts to reach out to him, and in defiance of his role in implementing a law passed by the voters, LePage was absent. His office and many of his agencies refused to take part in the committee's work, failing to appear at hearings or even answer written questions sent their way.
LePage is now using his own lack of interest in governing as a reason to slow the process. Fredette even had the gall to tell MPBN that the moratorium is necessary because LePage wasn't involved in the committee's work, forgetting to mention that his exclusion — the dereliction of duty from Maine's chief executive — was completely the governor's choice.
And while the pair apparently had concerns about the committee's process, they didn't take those concerns to the committee — Sen. Roger Katz, the committee co-chairman, first heard about the last-minute bill from a reporter.
As we speak, marijuana is being grown, sold and used — LePage and Fredette can't stop that. But they can bolster the black market, and inject more uncertainty into a process that already has communities scrambling for information.
If LePage's bill passes, it would push off regulations on retail sales even longer, allowing illegal growing and sales to flourish in its place. If neither bill passes, the law approved by voters in November, with its flaws and biases, will go into law.
That leaves the committee's bill, informed by many voices and hours of thoughtful debate and discussion. For months, Mainers concerned about this significant change in state law worked together to find the best way forward. Their efforts shouldn't be pushed aside on the whims of those who couldn't be bothered to take part.


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For any greatest hits collection there will be some quibbles. I would have left off the overly short "Long Ago and Far Away" (which seemed to be an idea for a song rather than a finished item, on which Taylor was accompanied by Joni Mitchell). Instead, I would have included "Mockingbird," on which Taylor sang with his then-spouse Carly Simon – assuming the rights were available for licensing from Elektra/Warner. And I would have preferred "Suite for 20G" instead of the live take on "Steamroller." Nevertheless, all of Taylor's hits – as documented by their Pop and Adult Contemporary peak chart positions – and several interesting lesser-known songs are found here.
"Honey Don't Leave L.A.," written by Danny Kortchmar, is one of the fun and unexpected selections in this compilation. Fortunately, "Her Town Too," co-written and performed by Taylor and the very talented J.D. Souther, is included. There's an interesting track, "Hard Times Come Again No More," which was recorded with Yo-Yo Ma, and a jaunty live version of the classic "Country Road." "Secret O' Life" – recorded live – is a nice surprise for those not previously familiar with it.
A word about the sound. This compilation was produced by Bill Inglot and mastered by Vic Anesini. Anesini has been involved in mastering several Legacy discs, including Over the Bridge of Time: A Paul Simon Perspective (1964-2011). Here, the Inglot-Anesini team has delivered a set of discs with a nice, warm mid-range tone that's generally pleasing to the ear. This collection is not a case where artificial "punch" and jarring loudness are added for dramatic effect. The sound is as soothing as Taylor's voice. And Taylor's and Kortchmar's guitar work is easily heard in the mix. There are a couple of tracks that sound a bit flat, as if one were listening to the songs over a set of television speakers. But all in all, it's a compilation that sounds consistently fine whether one is listening at home or in the car.
It's a bit of a puzzle as to why Inglot placed the songs in almost, but not quite, chronological order. Perhaps it has to do with the segues, deciding which song would sound best following another particular song. I would not change a thing about the song order on either disc.
This fresh look at Taylor's career that spans the years 1969 through 2007 reminds us that he is, like Paul Simon, a true American treasure. James Taylor's music has not just helped to – in the words of the liner notes – "define a generation," it helped a generation grow, survive and prosper even when times seemed to be at their worst ("Sweet dreams and flying machines in pieces on the ground.").


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10 Leadership Trends You Are Likely to See In 2023
By Thom Dennis, CEO of culture change and leadership development specialists, Serenity in Leadership.
After another incredibly tumultuous year and a recession on its way, leaders have been trying to steady the ship to navigate through the difficult times, but many are choosing to do more than survive and are aiming to get back to thriving beyond the profits, by focusing on culture, innovation and taking a long term view. These are the trends in good leadership you are likely to see in 2023.
1. Visionary Storytellers. I recently interviewed Dean Carter who led global HR and Shared Services at the ground-breaking company Patagonia and is now a Director of Griffith Foods, the global traceable and sustainable food ingredients experts. He said: "A leader for me is someone who has a compelling view of the future and their way of looking at the future is a very compelling thing to align behind. They also know their vision always has to be possible and the team need to be able to clearly see the actions that can be taken to get there." Dean argues that visionary leaders have a better way of communicating their mission and objectives and can harness their narrative in such a way that it makes people want to be a part of making that vision happen.
2. Walk The Walk. Leaders will regularly need to re-examine if they are on track and are still aligned with their mission statement, values and purpose, and leading clearly with those at the forefront. During tumultuous times we need responsible leaders more than ever. A recent study of nearly 700 US companies showed scant correlation between stated company values and employee perceptions of the organization so this will have to change in the very near future.
3. Superb Tacticians For the Future. Leaders understand they need to re-create a hybrid workplace where workers want to be, to see friends, explore ideas, make a difference, learn and find meaning. Do these things well, and retention problems will be eased. You have to make money to stay in business, but you keep employees during otherwise difficult times if they are engaged, learning, and increasingly enjoying themselves. As Dean said about culture: "If we're talking about making it fun, it probably isn't fun", and advocated for CEOs who don't take themselves too seriously.
4. Nurturers. This means taking a firm line on sharing the burdens, reducing toxicity and burnout in the workplace, and wanting the best for colleagues' mental and physical health. Being individual-employee-centric and offering flexibility and support are key.
5. High Cultural Intelligence. Senior executives and partners serve as a model for vision, purpose, and company culture and there is a 750% differential in profits at companies with aligned and mature cultures versus those that fail to cultivate their cultures. CQ is an easily learned and developed, but extremely important skill.
6. Build Better Teams. Leaders who have high-performing C-Suites say they are 42% more effective at managing complex initiatives, 31% more effective at delivering stakeholder value, and 30% more effective at attracting top talent. During times of transition, such as a merger or private equity deal, the quality of a business's management team is the most-cited reason for deal success and second for deal failure.
7. Innovators. Technology is always evolving, offering new opportunities to CEOs looking to transform their business. That's especially true when pursuing net-zero. It is also true for companies that are making the shift to put software at the heart of their business. Leaders will be looking for innovators with software experience and who want to explore the use of AI in the context of responsibility, trustworthiness and ethics. The trend is for an increasing number of members of the C-Suite to have software experience.
8. Empowerers. The best leaders are those who enable their people to make good decisions. Admiral Horatio Nelson is still today recognised as an inspirational leader and an incredible tactician. He knew that once the battle started, there would not be any possibility of communicating between ships so instead he empowered each of his captains to take decisions and risks. He did this by sharing his strategy and communicating in depth with them so they could act with autonomy because they really knew each other and understood the desired outcome. There has been a trend in leaders towards autocracy in recent years – this rarely works over a period of time and makes succession extremely difficult. Leaders need to empower, build morale and make their teams feel entrusted.
9. Clear Succession Plan. The leaders of 2023 understand that they need to listen and learn from others to improve and grow themselves. We simply cannot do it all ourselves. These leaders also know that at some stage someone is going to do it better than them and power sharing is in the best interest of everyone, including ourselves. Successful leaders will surround themselves not with sycophants but with people who will question them and provide alternative opinions, feedback and solutions.
10. Authentically Support Important Causes. In 2016 Patagonia announced that it would donate 100 percent of its global retail and online sales from the shopping event on Black Friday straight to grassroots organizations that work in local communities to "protect our air, water and soil for future generations". They made a record-breaking $10 million in sales during the event, a figure five times greater than expected, along with massive media coverage. As the cost of living and environmental crises rage on in 2023, expect to see leaders take bigger, more courageous and more meaningful leaps of faith to support important causes.
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Q: How do you request user input using Rx? I am writing a class that encapsulates a state machine that represents my applications attempts to communicate with my own web service. Basic states are disconnected, connecting, connected, and requiring credentials. I thought for good learning experience about using Rx to publish state changes with a BehaviorSubject (hopefully this in itself is good usage?). One of my states for this subject is the 'Requiring Credentials' where I need to prompt the user to provide a username and password before continuing. For the purposes of this exercise let us assume that the class is hosted in a Windows Console Application and that I want to prompt the user with
Console.WriteLine("Enter username");
var userName = Console.ReadLine();
Console.WriteLine("Enter password");
var password = Console.ReadLine();

As a result of my Rx BehaviorSubject hitting the state 'RequiresCredentials' and it should hit this every time this state is hit.
I have exposed the BehaviorSubject as itself (i.e. haven't hidden it behind an Observable interface or anything)
public BehaviorSubject<ConnectionState> State { get; }

and want this request for credentials to be blocking.
What process should I use for subscribing to this subject correctly, waiting for this input and finally returning control back to the calling thread?

A: If you're not using tasks or await, or anything asynchronous, Rx subscription code will observe on the same thread, and block if you're using blocking code. If you don't care about the input, then you can do a straight Subscribe. If you want to use the inputted username/password, then you can use Select. So this would work:
class Program
{
    static void Main(string[] args)
    {
        var subject = new BehaviorSubject<ConnectionState>(ConnectionState.Disconnected);

        var getCredentials = subject.Where(cs => cs == ConnectionState.RequiresCredentials)
            .Select(cs =>
            {
                Console.WriteLine("Enter username");
                var userName = Console.ReadLine();
                Console.WriteLine("Enter password");
                var password = Console.ReadLine();
                return Tuple.Create(userName, password);
            });
        using (var subscription = getCredentials.Subscribe())
        {
            Console.WriteLine("Changing to Connecting...");
            subject.OnNext(ConnectionState.Connecting);
            Console.WriteLine("Changing to RequiresCredentials...");
            subject.OnNext(ConnectionState.RequiresCredentials);
            Console.WriteLine("Connected.");
            subject.OnNext(ConnectionState.Connected);
        }

    }
}

enum ConnectionState
{
    Disconnected,
    Connected,
    Connecting,
    RequiresCredentials
}

It produces the following output:
Changing to Connecting...
Changing to RequiresCredentials...
Enter username
ThisIsMyUserName
Enter password
ThisIsMyPassword
Connected.

This is a rather backwards use of Rx though: If you're looking to use Rx in an iterative, procedural way, why don't you just use C# and save yourself complexity?

redpajama_set_name: RedPajamaStackExchange


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Check Out Yemi Alade's Distinctive Outfit
Written by Oluwatoyin Adeleye She just keeps turning heads! Yemi Alade shared this photo on her Instagram, wearing a unique outfit from the stables of...
Wizkid Features 2Baba & Tiwa Savage In New Singles
Written by Oluwatoyin Adeleye Wizkid has definitely kept busy since his return to Nigeria. The starboy is reported to have been working on new singles,non...
Dibs On Tiwa Savage's Success Story
Written by Clement Oluwasegun Superstar Afrobeat diva, Tiwa Savage has opened up her struggle and fearless determination to succeed. In a recent interview...
Burna Boy's Gram Is About The Coolest At The Moment!
Written by Oluwatoyin Adeleye If you haven't been on Burna Boy's Instagram lately, you might want to rush over there. His page is about the coolest page o...
#MotivationalMonday: Have You Heard Beyonce's 10 Rules To Success?
Written by Oluwatoyin Adeleye Music queen, singer, songwriter, record label owner, and actress (basically an entrepreneur) Beyonce, recipient of about 20 Gra...
D'banj Lands In Nairobi, Kenya For Koroga Festival
Written by Oluwatoyin Adeleye Kokomaster, D'Banj has landed in Nairobi, Kenya for the country's Koroga festival set to hold this evening. The singer a...
9ice's Former Wife, Toni Payne Finds Love Again
Written by Damilola Faustino Toni Payne who is the ex-wife of afro pop singer 9ice seems to have found love again. Toni, who used to be an artist mana...
Yemi Alade Sets New World Record
Written By Damilola Faustino YouTube, has named Yemi Alade's 'Johnny' music video as the most watched video by an African woman. The video, which ...
JAY-Z's Bonus Tracks Are Now Available on Tidal
Written By Damilola Faustino JAY-Z's 4:44 bonus tracks are now available for streaming on Tidal. The three additional tracks include: "Adnis," "Blue's...
Meek Mill Admits Breakup With Nicki Minaj Was A Loss
Written By Damilola Faustino Six months after Meek Mill and Nicki Minaj ended their relationship, it appears that the rapper has not gotten over the spli...
Fans & other celebrities GUSH over Maleek Berry!
Written by Tochi Wigwe First off, congratulations to Maleek Berry who sold out his first headline show at the Scala venue, London, last night! Fans as w...
Rick Ross Apologises For Loose Comment on Female Rappers
Written By Damilola Faustino During the week, Rick Ross made some controversial comments about why he has never signed a female rapper to MMG, his record lab...
Dammy Krane Credit Card Fraud Trial To Start August 1
Written By Damilola Faustino Dammy Krane, who has been accused of credit card fraud in the United States will appear in court for trial on August 1 at the Ju...
Lionel Richie And Charlie Puth May Be The Final Judges of American Idol
Written By Damilola Faustino Lionel Richie and Charlie Puth are in advanced talks to join Katy Perry and Ryan Seacrest on the judges' panel of the revival of...


text:
Angel di Maria: Man United the only club I'd leave Real Madrid for
Manchester United sign Angel di Maria in a British record £59.7m deal from Real Madrid on Tuesday evening
Angel di Maria has declared that Manchester United were the only club that could tempt the Argentine from Real Madrid after completing his move to Old Trafford.
The 26-year-old forward has signed a five-year deal with the 20-time English champions after United agreed a British record £59.7m fee with los Blancos.
I am impressed by the vision and determination everyone has to get this club back to the top – where it belongs
Di Maria, who completed his medical at the club's Carrington training ground on Tuesday, becomes the fourth signing of Louis van Gaal's reign.
Whilst the Argentina international was attracting plenty of interest from clubs across Europe, Di Maria insisted that the Red Devils were always his first choice.
"I am absolutely delighted to be joining Manchester United. I have thoroughly enjoyed my time in Spain and there were a lot of clubs interested in me, but United is the only club that I would have left Real Madrid for," Di Maria told United's website.
"Louis van Gaal is a fantastic coach with a proven track record of success and I am impressed by the vision and determination everyone has to get this club back to the top – where it belongs. I now just cannot wait to get started."
Di Maria has scored 22 goals in 124 La Liga appearances during four seasons at Madrid.
Alex Oxlade-Chamberlain backs Yaya Sanogo to shine for Arsenal
Louis van Gaal: 'Team player' Angel Di Maria is fantastic Man United addition


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dnsmasq
=======

The project uses `dnsmasq <http://www.thekelleys.org.uk/dnsmasq/doc.html>`_ to
configure each host to use :doc:`consul` for DNS.

Variables
---------

The dnsmasq role uses ``consul_dns_domain``, ``consul_servers_group``, and
``consul_dc_group`` defined in :doc:`consul`.

redpajama_set_name: RedPajamaGithub


An SUV crashed into a home on Camp Street in Middletown on Friday, April 5, 2019.
MIDDLETOWN — A woman crashed her SUV into a house on Camp Street on Friday afternoon, officials said.
The driver, traveling southbound in her Mercedes at about 11:50 a.m., crossed the center line onto the east shoulder of the roadway. The vehicle continued across the front lawn and into the home, according to police.
She was taken to Middlesex Hospital with minor injuries, officials said.
Police on scene said the woman possibly lost control of her brakes during the crash.
At least two rooms at the front of the ranch-style home at 98 Camp St. had been reduced to rubble Friday from the impact of the vehicle.
The house is about a quarter-mile from Washington Street/Route 66.
The Middletown building inspector was on scene to evaluate the integrity of the home.
The traffic unit is investigating the motor vehicle accident. Anyone with any information should call 860-638-4000.


text:
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My boys are hot chocolate snobs. 😉 And by snobs, I mean, they love just regular ole Swiss Miss Hot Chocolate. Pour the packet into a mug and cover with hot water, stir and serve. I've tried all kinds of fancy hot chocolates from chocolatiers and gourmet food companies. Nope. They ain't buying it. They like regular ole cocoa. They are simple fellas and I love them for it.
But sometimes you want to have a BIG batch on hand for your holiday gatherings. And this is that recipe! You literally just dump everything into the crock pot and stir occasionally. That's it. You can switch it to the "keep warm" setting and your friends and family can help themselves.
This is a super simple recipe that packs a wonderful chocolate flavor and is pure creamy deliciousness. It makes hot chocolate just a bit more special for the occasion and gets everyone into the holiday spirit. Be sure to check out my twists on this recipe for adult-only crowds!
In a 4-quart (or larger) slow cooker, combine all the ingredients. Give it a good stir. Updated to add: Some folks felt it was easier to heat up a cup of milk, then stir in the cocoa. It was mentioned that the cocoa blends in better this way. Then the warm milk mixture is then stirred in with the rest of the ingredients.
Cover and cook on low for about 2 hours. Stir occasionally as it warms up.
It's ready when all the chocolate chips have melted and mixture is warm.
Ladle into mugs and top with marshmallows or whipped cream and a mini candy cane!
Cook's Notes: For peppermint hot chocolate, add in a couple of teaspoons of peppermint extract instead of vanilla extract. For an adult beverage, try adding some Kahlua, Peppermint Schnapps or Rum Chata!
It's ready when all the chocolate chips have melted and mixture is warm.
For peppermint hot chocolate, add in a couple of teaspoons of peppermint extract instead of vanilla extract. For an adult beverage, try adding some Kahlua, Peppermint Schnapps or Rum Chata!
Hello! This looks delicious! Would using milk chocolate chips instead of semi-sweet ones work well? Or could this alter the taste?
I did this last year and it was too sweet. This year I will stick to the original recipe.
Best hot cocoa ever! Made it exactly per the recipe and did not heat the milk first.
I made this for NYE; I doubled the recipe and shouldn't have, because it has a huge yield! I had 2 cans of chocolate condensed milk on hand. Other than that, I followed the recipe and it was pure decadence . It's not diabetic friendly, but it sure can make you forget! Thank you for sharing.
Yay! Thanks so much Ruth! You can always pop it into the fridge and heat up any leftovers later if you have too much leftover 🙂 Happy New Year!
Hello! Can I ask how many people you think that doubling the recipe could have served?
Could I freeze hot chocolate? We like hot chocolate when we go ice fishing. This time we had some left over and I don't know if we will go again in 2-3 days. Would this make it last longerand would it degrade the hot chocolate?
Could you use unsweetened almond milk instead of the whole milk?
My question too! Has anyone tried this with almond milk??
I have a question about heating up the milk as well. Do I heat up just one of the 6 cups of milk or heat up each cup of milk?
It was a little confusing.
Tried the crockpot hot chocolate last night for company while having "Santa" visit. It was delicious and a big hit!!! Well worth your time to have REAL hot chocolate! Easy too!
We are doing a progressive dinner. My home is the last stop for dessert. I really want to serve this, it sounds so delicious.
What is the best way to do this. I will be gone from my house for 2 and 1/2 hours.
Substitute for sweetened condensed milk?


text:
import { Config } from 'protractor';

import { CucumberConfig } from '../../serenity-cucumber/cucumber_test_framework';
import { MochaConfig } from '../../serenity-mocha';
import { StageCrewMember } from '../../serenity/stage';

export interface SerenityFrameworkConfig extends Config {
    serenity?: {
        crew?: StageCrewMember[];
        dialect?: 'cucumber' | 'mocha';
    };

    cucumberOpts?: CucumberConfig;
    mochaOpts?: MochaConfig;
}


text:
\section{Introduction}
Since the pioneering theoretical proposal of a rectifying single-molecule
device \cite{Aviram1974} and the first charge transport measurements on single
molecules \cite{Reed1997,Smit2002}, many groundbreaking experiments have
explored fundamental physical aspects in these kinds of nanojunctions. They
involve the electrical conductance \cite{Nitzan2003,Xu2003}, thermoelectricity
\cite{Reddy2007,Cui2018}, energy dissipation \cite{Lee2013}, quantum
interference \cite{Garner2018,Miao2018} and electronic noise
\cite{Djukic2006,Karimi2016,Lumbroso2018}. All of these studies contributed
significantly to our current understanding of the phase-coherent electronic
charge transport at the nanoscale, thereby establishing the active research
field of molecular electronics \cite{Baldea2016, Cuevas2017,
  Moth-Poulsen2016}. One of the most appealing features of molecular junctions
is their tunability in terms of chemical synthesis, including molecular length
\cite{Hines2010}, conjugation \cite{Venkataraman2006,Mishchenko2010},
anchoring groups \cite{Park2007,Leary2015}, and chemical substituents
\cite{Venkataraman2007}, as well as the possibility to exert external control,
for instance through mechanical forces \cite{Vacek2015, Stefani2018} or
photons to trigger optically induced switching \cite{Dulic2003}.

Only recently the molecular junctions have been pushed into an entirely new
direction by measuring their thermal conductance \cite{Cui2019}. Since most
molecules exhibit a rather insulating, off-resonant charge transport behavior,
electronic contributions to the thermal conductance can typically be
disregarded \cite{Kloeckner2016,Kloeckner2017,Cui2019}. The thermal
conductance thus arises basically from phonons or photons
\cite{Kloeckner2017a}. Due to the recently established measurement scheme of
self-breaking single-molecule junctions \cite{Cui2019}, which will be
described further below, radiative heat transport plays no role, and the
phononic thermal conductance contribution is directly determined. This allows
to explore the physics of bosonic quasiparticles at the nanoscale. Similar to
the field of ``molecular electronics'' the upcoming field of ``molecular
nanophononics'' will benefit from the molecular tunability. Theoretical
suggestions have already been made to realize interference effects or to
adjust the thermal transport by use of anchoring groups and substituents
\cite{Markussen2013,Kloeckner2017,Kloeckner2016,Li2017,Famili2017}. With the
novel measurement techniques \cite{Cui2019}, the theoretical predictions are
now amenable to the experimental test.

The thermal transport through self-assembled monolayers of alkane molecules
has been studied by several research groups \cite{Wang2006, Wang2007,
  Meier2014}. Genuine single-molecule experiments eliminate crucial
uncertainties of such ensemble measurements, for example the number of
molecules contacted, the role of intermolecular interactions, possible defects
in the self-assembled monolayers or thickness variations due to surface
corrugation. Ref.~\cite{Cui2019} has successfully demonstrated
room-temperature measurements of the thermal conductance of gold-alkane-gold
single-molecule contacts. By detecting a length-independent thermal
conductance for dithiolated alkanes of different lengths at room temperature,
a basic fingerprint of the phase-coherent nature of heat transport in these
nanojunctions has been shown.

The key experimental challenge that has been overcome in Ref.~\cite{Cui2019}
is the detection of minute thermal currents through single-molecule junctions
at room temperature. Depending on the applied temperature difference, thermal
currents are on the order of picowatts, and a highly sensitive thermal
measurement scheme is needed that additionally ensures a high mechanical
device stability at the elevated temperatures. In order to measure the thermal
conductance at room temperature, the following advanced protocol has been
developed: In a first step, molecular junctions are characterized
electronically through a conventional electrical conductance histogram. The
information contained in the histogram is then used to identify
single-molecule junctions through the most probable single-molecule electrical
conductance. Electrical conductance-distance traces are now taken, but the tip
withdrawal is stopped, if a single-molecule junction is identified. At this
point the electrical conductance and the temperature of the tip, from which
the thermal conductance of the junction can be deduced, are monitored
simultaneously. After a waiting time on the order of seconds, the contact
finally breaks spontaneously. Due to the low thermal signal, a sophisticated
averaging scheme needs to be applied. Several hundred thermal conductance-time
traces, each 1.1~s in length, are aligned to the breaking point, identified by
the electrical conductance signal, and averaged. In this way a clear change in
the thermal conductance due to contact rupture is observed, which is identical
to the sum of the phononic and often negligible electronic thermal conductance
of the single-molecule junction.

While it would be desirable to measure a full thermal conductance-distance
trace, similar to what is possible in electrical conductance measurements,
with the newly developed protocol the single-molecule thermal conductance can
only be studied at the point of breaking. On the other hand, it is a clear
advantage that the measurement protocol determines the thermal conductance as
a difference of thermal conductances before and after the thermally induced
contact rupture. Since the electrode separation remains unchanged, radiative
thermal conductance contributions cancel out. In Ref.~\cite{Cui2019} the
alkane chains C2-C10, containing two to ten carbon atoms, have been
analyzed. For C2 the electronic contribution to the thermal conductance was
significant, but it could be neglected for C4-C10. For these reasons we focus
here on phonon thermal conductance calculations for C4-C10. As the experiment
determines the phononic thermal conductance as a mean value over a time series
of junction structures before contact rupture, it is important to
theoretically explore the magnitude of geometry-induced variations of the
thermal conductance. We address this topic in the present work.

Our study is structured as follows. We commence with a description of the
theoretical methods in Sec.~\ref{sec-theory}, where we introduce the DFT-NEGF
method for phonon transport in Sec.~\ref{sec-theory-DFT+NEGF} and the NEMD
approach in Sec.~\ref{sec-theory-NEMD}.  The results are presented in
Sec.~\ref{sec-Alkane-Variation}. In particular, Sec.~\ref{sec-Alkane-Geometry}
deals with different absorption sites of the alkanedithiols on the electrodes
and different electrode orientations. Next, we investigate the influence of
gauche defects on transport in Sec.~\ref{sec-Alkane-Defects} and how they
respond to strain. Sec.~\ref{sec-Alkane-NEMD} adds an analysis of temperature
effects via the NEMD approach to the previous two DFT-NEGF studies. We close
with the conclusions in Sec.~\ref{sec-conclusions}.

\section{Theoretical methods}\label{sec-theory}

In order to give a comprehensive picture, we take advantage of two
complementary approaches to calculate the thermal conductance of
single-molecule junctions. To be precise, we first study the phase-coherent
phonon transport in the spirit of the Landau-B\"uttiker scattering theory
using NEGF techniques, where the device-specific parameters are obtained from
DFT as implemented by us and described in
Refs.~\cite{Buerkle2015,Kloeckner2019}. The phonon thermal conductance of the
nanoconstriction is calculated as a linear-response property based on the
harmonic approximation. Anharmonic scattering, for instance from phonon-phonon
interactions, is explicitly neglected, and the geometries are obtained as
energetically favorable configurations at temperature $T=0$.

These studies are complemented by NEMD simulations. In comparison to the
ab-initio approach, this method offers several advantages. NEMD naturally
considers the nonequilibrium situation and temperature gradients inside the
junction, i.e., the heat transport can be described for high applied
temperature differences between left and right electrodes. Since the
experiments measure the thermal conductance in the linear-response regime
\cite{Cui2019}, this is not relevant however, and we apply NEMD and DFT-NEGF
in that limit. Whereas the DFT-NEGF methodology is restricted to a few
hundreds of atoms for practical computational efforts, with the molecular
dynamics (MD) simulations
atom numbers on the order of many thousands can easily be
handled. Importantly, anharmonic effects are taken into account in a
non-perturbative manner. These anharmonic effects lead to phonon-phonon
interactions or the temperature-dependent lattice expansion. The
time-dependent simulations imply a sampling of the geometrical phase space.
The major drawback can be seen in the need for empirical interatomic
potentials, which are not universal and often optimized for special
purposes. This becomes most evident, when interface structures are considered
at the atomic scale. Due to lack of chemical information conventional
potentials then tend to fail to describe geometries reliably. Although there
are improved potentials, they come along with higher computational costs. In
contrast, DFT-based methods are known to provide reliable geometries at atomic
scales. Since MD uses classical statistics, another disadvantage is that
quantum effects are not taken into account. This limits the applicability to
thermal energies above the material-specific highest phonon energies. For
gold, our DFT calculations yield a cutoff at around 20~meV, which is on the
order of the Debye energy of 15~meV. This corresponds to temperatures above
around 200~K, justifying the application in this work.

In short, DFT-NEGF and NEMD approaches complement each other. Therefore both
will be used in our room-temperature study. In the following, we will present
them in greater detail.

\subsection{Phonon transport in the Landau-B\"uttiker scattering theory using DFT parameters}\label{sec-theory-DFT+NEGF}

For the calculation of heat transport via phonons in the phase-coherent
regime, we consider the Hamiltonian due to small displacements $\{Q_{\xi}\}$
of atoms away from their equilibrium position $\{R_{\xi}^{(0)}\}$
\begin{equation}
  \hat H = \frac{1}{2} \sum_{\xi} \hat{p}_{\xi}^{2} + \frac{1}{2\hbar^{2}}
  \sum_{\xi\chi} \hat{q}_{\xi} K_{\xi\chi} \hat{q}_{\chi}.
\end{equation}
In this expression we have introduced the mass-weighted displacement
operators $\hat{q}_{\xi} = \sqrt{M_{\xi}}\hat{Q}_{\xi}$ and the mass-scaled
momentum operators $\hat{p}_{\xi}=\hat{P}_{\xi}/\sqrt{M_{\xi}}$.  They obey
the usual commutation relations: $[\hat{q}_{\xi},\hat{p}_{\chi}] =
\mbox{i}\hbar\delta_{\xi\chi}$ and $[\hat{q}_{\xi},\hat{q}_{\chi}] =
     [\hat{p}_{\xi},\hat{p}_{\chi}]=0$, where $\xi=(j,c)$ denotes a Cartesian
     component $c=x,y,z$ of atom $j$ at position $\vec{R}_{j} =
     \vec{R}_{j}^{(0)}+\vec{Q}_{j}$. As the system-specific quantity we
     calculate the dynamical matrix $K_{\xi\chi} = \hbar^{2}
     \partial_{\xi\chi}^{2}E_{\rm DFT}/\sqrt{M_{\xi}M_{\chi}}$ as the
     mass-weighted second derivative of the DFT total ground state energy
     $E_{\rm DFT}$ with respect to the Cartesian atomic coordinates.

For the transport calculation we divide the dynamical matrix into different
subsystems, namely a central (C) scattering region and the two semi-infinite
left (L) and right (R) electrodes
\begin{equation}
  \boldsymbol{K}=\left(\begin{array}{ccc}
    \boldsymbol{K}_{\mathrm{LL}} & \boldsymbol{K}_{\mathrm{LC}} & \boldsymbol{0}\\
    \boldsymbol{K}_{\mathrm{CL}} & \boldsymbol{K}_{\mathrm{CC}} & \boldsymbol{K}_{\mathrm{CR}}\\
    \boldsymbol{0} & \boldsymbol{K}_{\mathrm{RC}} & \boldsymbol{K}_{\mathrm{RR}}
  \end{array}\right).
  \label{eq-Kmatrix}
\end{equation}
In our implementation we extract the elements
$\boldsymbol{K}_{X\text{C}},\boldsymbol{K}_{\text{C}X},\boldsymbol{K}_{\text{CC}}$
with $X=\text{L,R}$ from an extended central cluster, while the elements
$\boldsymbol{K}_{\text{LL}}$ are obtained from a separate bulk calculation. To
account for the acoustic sum rule $K_{jc,jc'}=-\sum_{j'\neq j}K_{jc,j'c'}
\sqrt{M_{j'}/M_j}$, where $j,j'$ indicate atoms and $c,c'$ Cartesian
components, we correct the surface elements as described in
Ref.~\cite{Kloeckner2019}.  Since we assume a vanishing coupling between the
two leads, the thermal conductance can be calculated as the linear-response
coefficient in a heat current formula \cite{Rego1998, Mingo2003, Yamamoto2006}
and reads
\begin{equation}
  \kappa_{\rm pn}(T) = \frac{1}{h} \int_{0}^{\infty} E \tau_{\rm pn}(E)
  \frac{\partial n(E,T)}{\partial T} \mathrm{d}E.
  \label{eq-kpn}
\end{equation}
Here $n(E,T)=[\exp(E/k_{\rm B}T)-1]^{-1}$ represents the Bose function and
$\tau_{\rm pn}(E)$ is the phonon transmission function. In the framework of
NEGF it is given by \cite{Mingo2003,Buerkle2015}
\begin{equation}
  \tau_{\rm pn}(E) = \mathrm{Tr} \left[ \boldsymbol{D}_{\mathrm{CC}}^{\textrm{r}}(E)
    \boldsymbol{\Lambda}_{\textrm{L}}(E) \boldsymbol{D}_{\mathrm{CC}}^{\textrm{a}}(E)
    \boldsymbol{\Lambda}_{\textrm{R}}(E)\right],
  \label{eq-tauph}
\end{equation}
where $\boldsymbol{D}_{\mathrm{CC}}^{\textrm{r,a}}(E)$ are the retarded and
advanced phonon Green's functions of the center.  They are defined as
$\boldsymbol{D}_{\rm CC}^{\rm a}(E) = \boldsymbol{D}_{\rm CC}^{\rm
  r}(E)^{\dagger}$ and
\begin{equation}
  \boldsymbol{D}_{\mathrm{CC}}^{\mathrm{r}}(E) = \left[\left(E+i\eta
    \right)^{2}\boldsymbol{1}_{\textrm{CC}} - \boldsymbol{K}_{\textrm{CC}} -
    \boldsymbol{\Pi}_{\textrm{L}}^{\mathrm{r}}(E) -
    \boldsymbol{\Pi}_{\textrm{R}}^{\mathrm{r}}(E) \right]^{-1}
\end{equation}
with the infinitesimal parameter $\eta>0$. The scattering rate matrices
\begin{equation}
  \boldsymbol{\Lambda}_{X}(E)= i
  \left[\boldsymbol{\Pi}_{X}^{\mathrm{r}}(E)-\boldsymbol{\Pi}_{X}^{\mathrm{a}}(E)\right]
\end{equation}
are related to the corresponding embedding self-energies
\begin{equation}
  \boldsymbol{\Pi}_{X}^{\mathrm{r}}(E) = \boldsymbol{K}_{\textrm{C}X}
  \boldsymbol{d}_{XX}^{\mathrm{r}}(E) \boldsymbol{K}_{X\mathrm{C}},
\end{equation}
which describe the coupling between the C region and electrode $X$. In the
expressions $\boldsymbol{\Pi}_{X}^{\textrm{a}}(E) =
\boldsymbol{\Pi}_{X}^{\textrm{r}}(E)^{\dagger}$ and $\boldsymbol{d}_{XX}^{\rm
  r}(E)= [ (E+i\eta)^{2}\boldsymbol{1}_{XX} -
  \boldsymbol{K}_{\textrm{XX}}]^{-1}$ is the surface Green's function of lead
$X=\text{L},\text{R}$, which we calculate using the decimation technique
explained in Refs.~\cite{Pauly2008,Guinea1983}.

To better understand heat transport, we consider the decomposition of the
total phonon transmission of Eq.~(\ref{eq-tauph}) into contributions of
transmission eigenchannels, $\tau_{\rm pn}(E) = \sum_i \tau_{{\rm
    pn},i}(E)$. The coefficients $\tau_{{\rm pn},i}(E)$ are the eigenvalues of
the phonon transmission probability matrix $\boldsymbol t_{\rm pn}(E)
\boldsymbol t^{\dagger}_{\rm pn}(E)$, where $\boldsymbol t_{\rm pn}(E) =
\boldsymbol \Lambda^{1/2}_{\rm R}(E) \boldsymbol D_{\rm CC}^{\rm r}(E)
\boldsymbol \Lambda^{1/2}_{\rm L}(E)$ is the phonon transmission amplitude
matrix.  In this way on gets insight into the number of eigenchannels, which
are important for heat transport at a specific energy, and a visualization of
the transmission eigenchannels yields information on how the vibrational
energy is transported through the nanojunctions. For a detailed discussion of
the methodology, we refer to Ref.~\cite{Kloeckner2018}.

Another useful quantity is the cumulative thermal conductance
\begin{equation}
  \kappa^{\mathrm{ c}}_{\mathrm{ pn}}(E,T)= \frac{1}{h} \int_{0}^{E} E' \tau_{\rm ph}(E')
  \frac{\partial n(E',T)}{\partial T} \mathrm{d}E',
  \label{eq-kcpn}
\end{equation}
defined as the thermal conductance at temperature $T$ due to phonon modes up
to the given energy $E$. It provides information on how vibrational modes
contribute to the total thermal conductance.

For the DFT calculations we use TURBOMOLE V7.1
\cite{TURBOMOLE,Deglmann2002,Deglmann2004}, employ the Perdew-Burke-Ernzerhof
PBE exchange-correlation functional \cite{Perdew1992,Perdew1996} and the
"default2" basis set of split-valence-plus-polarization quality def2-SV(P)
\cite{Weigend2005} together with the corresponding Coulomb fitting basis
\cite{Weigend2006}. In order to accurately determine the vibrational energies
and force constants, we use very strict convergence criteria. In particular,
total energies are converged to a precision of better than $10^{-9}$~a.u.,
whereas geometry optimizations are performed until the change of the maximum
norm of the Cartesian gradient is below $10^{-5}$~a.u.. For the transmission
calculations we use $32\times32$ $k$-points transverse to the direction of
transport and $\eta=10^{-5}$~a.u..

\subsection{Phonon transport in NEMD}\label{sec-theory-NEMD}

\begin{figure}
  \centering \includegraphics[width=1.0\columnwidth]{Fig1.pdf}
  \caption{Geometry used in the NEMD simulations. The outermost atoms (marked
    by a black line above the corresponding atomic planes) are fixed to
    prevent a collapse of the system. They are followed by the atoms that are
    connected to the thermostats (red and blue) and held at constant
    temperatures of $T_{\text{L}}$ and $T_{\text{R}}$. The flexible electrode
    reservoir atoms (orange) on the left (L) and right (R) are bridged by a
    central (C) junction part (gray), containing gold tip structures and the
    alkane molecule.}
  \label{fig-NEMD-Setup}
\end{figure}

As an alternative to the calculation of the thermal conductance based on the
DFT-NEGF methodology, MD offers different possibilities to predict the heat
current at the atomistic level. Generally speaking, the MD methods can be
classified into two different subgroups, namely equilibrium MD and NEMD
\cite{Schelling2002}. While in equilibrium MD one computes transport
properties from correlation functions using the Green-Kubo formalism, in NEMD
the system is driven out of equilibrium and the response is calculated
directly. In principle, with either method both
bulk~\cite{Schelling2002,Mueller-Plathe1997,Ciccotti1980} and
interface~\cite{Landry2009,Chalopin2012,Barrat2013,Merabia2012} thermal
conductivities can be calculated. However, all of the MD methods require a
certain minimal amount of atoms to avoid finite-size effects
\cite{Sellan2010,Liang2014,Wang2017}.

In this work we use a direct NEMD approach, where the nonequilibrium situation
is realized by maintaining two spatially separated regions at a constant
temperature difference using thermostats, see Fig.~\ref{fig-NEMD-Setup}. Our
simulations are done with the LAMMPS software code \cite{Plimpton1995}.

A crucial factor in MD simulations is the choice of the interatomic
interaction potentials. Calculations of heat transfer through hybrid
metal-organic interfaces have used a Morse potential to describe the
sulfur-gold bond \cite{Luo2010, Soussi2015}. This kind of parametrization is
useful to characterize the binding situation in a self-assembled
monolayer~\cite{Luo2010, Ong2014, Majumdar2015}. In single-molecule junctions,
however, we find that these potentials are incapable of describing the
chemical bond at the metal-molecule contact correctly but lead to an
overcoordination at the sulfur atom, which tends to bind to too many gold
atoms. Additionally, covalent intramolecular interactions are often treated in
the harmonic approximation \cite{Luo2010,Soussi2015,Ong2014,Majumdar2015}. In
this work, we employ a reactive force field (REAXFF)
\cite{Russo2011,Senftle2016}, which is based on the concept of bond order to
model bonded and non-bonded interactions between atoms. Importantly, it can
describe both bond breaking and bond formation, and all interatomic
interactions in the systems are anharmonic.

Figure~\ref{fig-NEMD-Setup} shows a starting geometry of our NEMD
simulations. We employ periodic boundary conditions perpendicular to the
direction of transport and fixed boundary conditions parallel to it. The
outermost atoms on each side, indicated by the black line above the geometry,
are held fixed to avoid a collapse of the system. These regions are followed
by several atom rows, marked by the red and blue lines, where thermostats are
applied that keep these regions at constant temperatures. In detail we use two
velocity rescale thermostats (with \emph{fraction} factor $\alpha=0.8$ und
\emph{window}$= 0.01$~K) to maintain temperatures at $T_{\text{L}}$ and
$T_{\text{R}}$, as described in Ref.~\cite{Moehrle2019}. The largest part of
the simulation box consists of the L and R electrode atoms, indicated by the
orange lines. To avoid finite-size effects, we have included in these regions
so many atoms, that the phononic density of states on each side closely
resembles that of bulk.  Similar to the DFT-NEGF formalism we define all atoms
in between the leads as C part, marked in gray.

Since we are investigating a nonequilibrium situation, we need to take
thermal expansion into account. The temperature difference in the L and R
regions leads to a corresponding difference in lattice constants in the
electrodes. In order to distribute strain effects equally over the whole
junction structure, we therefore determine the volume of the simulation box
from the effective lattice constant
\begin{equation}
  a_{\mathrm{eff}}=\sqrt[3]{\dfrac{a_{\mathrm{L}}^3+a_{\mathrm{R}}^3}{2}},
\end{equation}
where $a_X$ are bulk lattice constants at temperature $T_X$.

In order to calculate a thermal conductance that is comparable to the DFT-NEGF
method, the starting point for the C part in the NEMD simulations coincides
with the DFT geometry of junction type 1 (JT1), compare
Figs.~\ref{fig-NEMD-Setup} and \ref{fig-ContactGeo}. Large electrodes,
oriented along the (111) direction, in the L and R regions are matched to the
inner gold pyramid structures. While this procedure ensures geometries in C
that are similar to JT1, the junction is likely to be in a different strain
situation. This is attributed to differences in equilibrium interatomic
distances between DFT and the REAXFF. Additionally, the thermal expansion
modifies interatomic equilibrium distances in the NEMD simulations, as
discussed in the previous paragraph. The L and R regions in
Fig.~\ref{fig-NEMD-Setup} are five unit cells long, when seen along the
transport direction. Regions, where thermostats are applied, are one unit cell
thick, and the simulation box is enclosed by two rows of fixed atoms on each
side. In the transverse directions we use 12 unit cells, oriented along
$(\bar{1}\bar{1}2)$ and $(1\bar{1}0)$ crystallographic directions,
respectively. The NEMD junction geometry consists on each side of 384 fixed
atoms and 576 atoms in the parts coupled to thermostats. Furthermore, 2880
atoms reside in L and R parts, respectively. With the 4 gold atoms in the
pyramidal gold structures of each side and the variable number of atoms in the
dithiolated alkane chains C4-C10, this adds up to more than 7700 atoms.

For the integration of Newton's equation of motion, we use the velocity-Verlet
algorithm \cite{Swope1982}. We perform the NEMD simulations as follows. Apart
from the fixed atom regions, random velocities are assigned to all atoms in
the junction to yield a Gaussian distribution centered at 300~K. We start with
1~ns of equilibration with temperatures in the thermostats set to
$T_{\text{L}}=T_{\text{R}}=300$~K. Next we increase the temperature of the
left thermostat $T_{\text{L}}$ by the desired temperature difference $\Delta
T$ to $T_{\text{L}}=T_{\text{R}}+\Delta T$ over 1~ns. After an additional
equilibration time of 1~ns, we perform a time evolution over 4~ns, which
constitutes the actual simulation run. The time step chosen for the C4-derived
junction is 0.5~fs and 1~fs for C6-C10. In the NEMD simulations the separation
between the fixed layers is held constant, i.e.\ no pulling process is
performed.

The thermal conductance is calculated according to
\begin{equation}
  \kappa_{\mathrm{pn}}= \frac{J}{\Delta T}=\frac{\Delta E}{\Delta t \Delta T},\label{eq-kpn-NEMD}
\end{equation}
where $J=\Delta E/\Delta t$ is the steady-state heat current. Overall,
$\kappa_{\text{pn}}$ is thus obtained from the energy $\Delta E=(-\Delta
E_{\text{L}}+\Delta E_{\text{R}})/2$ supplied to the system by the thermostats
L and R per time step $\Delta t$, divided by the temperature difference
$\Delta T=T_{\text{L}}-T_{\text{R}}$. Details of the procedure are described
in Ref.~\cite{Moehrle2019}. In practice, we cumulate the output of the
thermostats $\Delta E$ over the simulation time $t=N\times\Delta t$ of $N$ MD
time steps and extract the heat current $J$ as the slope of a linear fit to
$\Delta E^{\text{c}}(t)=\sum_{i=1}^N\Delta E(i \times \Delta t)$. In the
simulations, we print out $\Delta E^{\text{c}}(t)$ every 2~ps.

\section{Variability of the phonon thermal conductance}\label{sec-Alkane-Variation}

Let us in the following discuss the phonon thermal conductance of
single-molecule junctions formed from dithiolated alkanes with 4-10 CH$_2$
units, hereafter named C4-C10, contacted by two gold electrodes. Since the
electronic contribution is negligible, the phonon thermal conductance is the
relevant property that is measured in novel heat transport experiments
\cite{Cui2019}. We quantify here the influence that different geometrical
variations exert on the phonon thermal conductance of single-molecule
junctions. These are the adsorption sites of the sulfur anchors on the gold
electrodes and the electrode orientation in Sec.~\ref{sec-Alkane-Geometry},
and the influence of gauche defects and strain in
Sec.~\ref{sec-Alkane-Defects}. In these two sections, we use the DFT-NEGF
approach. Finally, in Sec.~\ref{sec-Alkane-NEMD}, we study the effect of
thermally induced geometry variations with the help of the NEMD method.

\subsection{Adsorption site and electrode orientation}\label{sec-Alkane-Geometry}

\begin{figure}[t]
  \begin{center} \includegraphics[width=1.0\columnwidth]{Fig2.pdf} \end{center}
  \caption{(a) Different types of junction geometries (JT1-JT4) used for
    estimating the variability of $\kappa_{\text{pn}}$ in dependence on the
    molecule-electrode contact and the electrode orientation, here shown for
    C6. (b) Phonon thermal conductance for each junction type, as determined
    with the DFT-NEGF method, and the average taken over the values of
    JT1-JT4.}
  \label{fig-ContactGeo}
\end{figure}

To better understand the size of variability of the phonon thermal conductance
in single-molecule junctions, we start by determining $\kappa_{\text{pn}}$ for
different junction types with the DFT-NEGF approach. The junctions have been
constructed by varying the binding position of the molecular sulfur termini on
the gold electrodes as well as the orientation of the metal electrodes with
respect to the heat transport direction. Sulfur atoms on both ends are bonded
to a single gold tip atom in atop position for JT1, two gold atoms in bridge
position for JT2 and JT3, and three gold atoms in a hollow position in
JT4. The electrode orientations are $(111)$ for JT1 and JT4, $(110)$ for JT2
and $(100)$ for JT3.  The various contact geometries are displayed in
Fig.~\ref{fig-ContactGeo}(a) for C6. To provide a meaningful comparison among
different junction types, JT1-JT4 use fully extended, straight alkane
chains. They are built based on the same protocol, which minimizes strain
effects by first optimizing the molecule connected to one gold tip structure
and then attaching a gold tip on the other side symmetrically and reoptimizing
the geometry of the full molecular junction. Within one junction type, all the
alkanes of different length show a comparable geometry. The computed phononic
thermal conductance is depicted in Fig.~\ref{fig-ContactGeo}(b) and found to
be in the range of 30 to 50~pW/K with mean values around 35 to 40~pW/K. We
note that this data has been presented in ``Extended Data Table 1'' of
Ref.~\cite{Cui2019}.  As discussed there, the thermal conductances are
somewhat larger than experimentally detected, since we assume a situation with
low mechanical strain. Instead, at the experimentally relevant breaking point,
the mechanical tension can pull out gold atoms from the soft electrodes,
reducing $\kappa_{\text{pn}}$.

\begin{figure*}[t]
  \begin{center} \includegraphics[width=1.0\textwidth]{Fig3.pdf} \end{center}
  \caption{Total phonon transmission $\tau_{\text{pn}}(E)$ resolved into
    eigenchannel contributions. For JT1-JT4 the transmissions
    $\tau_{\text{pn},i}(E)$ of the three most transmissive eigenchannels
    $i=1,2,3$ are depicted as a function of energy for C10 in panels (a)-(d),
    respectively. In the inset of each panel, a static picture of the
    eigenchannel $i=1$ with the highest transmission is shown for two energies
    that are indicated by a vertical green line.}
  \label{fig-TransGeo}
\end{figure*}

The length-independent thermal conductance can be understood by studying the
phonon transmission \cite{Kloeckner2016,Cui2019}, which gives the probability
of a phonon to be transmitted elastically, i.e.\ at a specified energy, from
one electrode to the other through the alkane molecule. As visible in
Fig.~\ref{fig-TransGeo} for C10, $\tau_{\text{pn}}(E)$ exhibits resonances
with positions and widths that vary with contact geometry. The transmission
vanishes for energies above around $E_{\text{max}}=20$~meV, which corresponds
to the highest phonon energies of gold and is comparable to the Debye energy
of 15~meV \cite{Ashcroft1976}. Through the nearly constant factor $\partial
n(E,T)/\partial T$ in Eq.~(\ref{eq-kpn}), the transmissions in the range from
0 to $E_{\text{max}}$ contribute almost equally to $\kappa_{\text{pn}}$ at
$T=300$~K. Transmission resonances in this energy interval arise from
center-of-mass motions of the alkanes between the gold electrodes or molecular
vibrations with low energy. The longer the molecule, the more low-energy
vibrational modes will overlap with the phonon density of states of gold,
leading to an increasing number of transmission resonances between 0 and
$E_{\text{max}}$. At the same time transmission resonances become more narrow
for the longer alkanes due to a reduced electrode-molecule linewidth
broadening. The balance between both effects provides an intuitive explanation
for the rather length-independent phonon thermal conductance, as computed here
and measured in Ref.~\cite{Cui2019}.

To provide more insight into the origin of the thermal conductance variations,
we resolve in Fig.~\ref{fig-TransGeo} the transmission through C10 for the
whole series of junction types into contributions of the three most
transmissive eigenchannels. Irrespective of the junction type we observe that
two eigenchannels dominate the transmission, while a third one gives only
small contributions. With respect to the position and width of the individual
transmission resonances, there is a lot of change between different
junctions. Since transmission resonances are linked to the vibrational
structure of the junctions, they will sensitively depend on the precise
contact geometry, in particular the coupling of the molecule to the gold
electrodes. As a general feature, we find however that molecular
center-of-mass motions tend to yield peaks in the lower part of the energy
range between 0 and $E_{\text{max}}$, while molecule-internal vibrations are
responsible for resonances in the upper part.

To quantify geometry-dependent changes of vibrational modes, we search for
eigenchannels with similar shape in the energy range of nonvanishing
transmission of Fig.~\ref{fig-TransGeo}. We restrict this analysis to the most
transmissive first eigenchannel of JT1 at energies of 12.05 and 16.02 meV. On
the molecule the vibrations involved can be classified as out-of-plane and
in-plane modes, respectively, if we consider the plane spanned by the
molecular backbone of sulfur and carbon atoms. Both eigenchannels show two
characteristic sign changes when going from one end of the molecule to the
other, which we use to identify the corresponding eigenchannels in the other
junctions types. As indicated in each panel by insets and vertical green
lines, we find the position of the corresponding modes at 13.65 and 15.80~meV
for JT2, 13.16 and 16.05~meV for JT3, and 12.78 and 16.43~meV for JT4. While
we observe only moderate shifts in energy, the peak widths as well as the peak
heights may differ substantially, which exemplifies the crucial impact of
contact details on phonon transport.

\subsection{Molecule-internal defects and mechanical strain}\label{sec-Alkane-Defects}

\begin{figure*}[bt]
  \includegraphics[width=0.9\textwidth,clip]{Fig4.pdf}
  \caption{(a) Phonon thermal conductance $\kappa_{\text{pn}}$ vs.\ electrode
    displacement for the C10 chain containing gauche defects. Arrows indicate
    the thermal conductance of the four geometries visualized in the
    inset. (b) Corresponding pulling curves for the alkanes C4-C8. (c)
    Transmission resolved into eigenchannels for the three geometries labeled
    D1, D2, and D3 in panel (a), together with the cumulative thermal
    conductance of these junctions. (d) Thermal conductance of C4-C10,
    calculated as an average over the whole pulling curves shown in panels (a)
    and (b).}
  \label{fig-Defects}
\end{figure*}

In the previous section we focused on the thermal conductance of alkane chains
in a straight configuration. However, alkane chains are known to exhibit
geometrical defects, which can be thermally activated. In a study of
gold-alkane-gold junctions using ab-initio MD simulations \cite{Paulsson2009},
the authors related a peak in the histogram of the electrical conductance to
these defects. Furthermore they pointed out that upon stretching of the system
all defects vanish. For this reason the alkanes are expected to exhibit a
straight configuration before breaking of the contact. More recently these
defects have been shown to reduce the thermal conductance in comparison to
straight chains in a work employing graphene leads \cite{Li2015}. The authors
suggested to exploit the mechanism to realize a mechanically driven thermal
switch.

To test the influence of molecule-internal disorder on the phonon thermal
conductance of C4-C10, we generated chains containing defects by arbitrarily
varying torsional angles in the carbon backbone. As described in
Sec.~\ref{sec-Alkane-Geometry}, we set up the junction in the usual way by
first relaxing the twisted chain on top of one electrode and then
symmetrically attaching a gold pyramid by point mirroring at the free thiol
group. The geometries, which exhibit atomically sharp tips similar to JT1 in
Fig.~\ref{fig-TransGeo}, are then stretched to explore their response to
different strain conditions. We displace electrodes along the distance vector
connecting the gold tip atoms with increments of $0.5~\text{a.u.}\approx
0.265$~\AA.

Figure~\ref{fig-Defects}(a) shows the pulling of the alkane chain with 10
CH$_2$ units. Initially, the alkane exhibits four gauche defects. Since the
gauche defects appear in pairs, the alkane can be described as consisting of
three straight segments. In this initial stage the thermal conductance varies
smoothly around 20-30~pW/K, while the alkane adjusts continuously to the
increasing electrode separation. The region ends at a displacement of 0.24~nm
with a jump in $\kappa_{\text{pn}}$. Here the geometry of the alkane chain
changes, two gauche defects vanish, and the remaining pair splits the chain
into two straight segments. After two additional displacement steps, leading
to a decreased thermal conductance due to the induced strain, an additional
jump occurs at a displacement of 0.32~nm. From that moment on the chain is
defect-free. Further pulling leads basically to a continuous decrease of the
thermal conductance, before the contact finally breaks at an Au-Au bond. A
similar behavior is observed for the other chain lengths with 4-8 CH$_2$
segments, depicted in Fig.~\ref{fig-Defects}(b). Again defects in C4-C8 vanish
upon pulling, as it is evident from the discontinuous behavior of the thermal
conductance. In all examples the thermal conductance of the fully extended
configuration is larger than that of geometries with defects. We note that in
some cases studied in Fig.~\ref{fig-Defects}, Au chains form during the
pulling process, namely for the C4, C6 and C8 junctions. The formation of
chains depends sensitively on the starting configuration in the DFT
simulations, as discussed in Ref.~\cite{Cui2019}.

To better understand the origin of the reduction of $\kappa_{\text{pn}}$
through the torsional gauche defects, we show in Fig.~\ref{fig-Defects}(c) the
eigenchannel-resolved transmission of three examples with 4, 2, and 0
defects. The geometries of the junctions are depicted as insets, and their
thermal conductance values are indicated by arrows and labeled by increasing
displacement as D1, D2 and D3 in Fig.~\ref{fig-Defects}(a). In the two
examples with defects, D1 and D2, phonons within a different energy range are
responsible for the reduced conductance as compared to D3. In D1 this energy
range is located at about 13-17 meV, for D2 the reduced transmission results
from around 4-7~meV. This is particularly evident by analyzing the cumulative
thermal conductance. Here, the curves D1 and D3 almost coincide up to an
energy of around 13 meV but deviate above. A comparison of D2 and D3, on the
other hand, reveals the main difference to start occurring around 4~meV,
whereas after 7~meV the offset in $\kappa_{\text{pn}}^{\text{c}}$ stays more
or less constant.

Finally, we show in Fig.~\ref{fig-Defects}(d) the mean thermal conductance of
C4-C10, calculated by averaging over all the thermal conductance values in the
contact regime of the pulling process with $\kappa_{\text{pn}}>
0.1$~pW/K. Highest and lowest thermal conductance values in this range are
indicated through arrow bars. The mean thermal conductance represents an
average over several strain conditions and geometrical configurations, and it
shows a nearly length-independent value of 20-30 pW/K. Of course, the starting
point for taking the average is somewhat arbitrary in this case, since it is
determined by the chosen starting configuration. Interestingly, however, the
values predicted for the thermal conductance are similar to what we have
computed in Ref.~\cite{Cui2019} at the point of contact rupture. Indeed,
Fig.~\ref{fig-Defects}(a) and \ref{fig-Defects}(b) show that junctions with
defects in the alkane chain can feature a similar thermal conductance as
junctions with straight chains before the point of rupture.

\subsection{Thermally induced geometry changes}\label{sec-Alkane-NEMD}

\begin{figure}[tb]
  \begin{center} \includegraphics[width=1.0\columnwidth,clip]{Fig5.pdf} \end{center}
  \caption{(a) Cumulated output of the thermostats $\Delta E^{\text{c}}$ over
    time for a C6 junction. The red line shows the linear fit used to
    calculate the thermal current $J$. For each nanosecond interval a
    representative geometry is depicted. The non-zero value of $\Delta
    E^{\text{c}}$ at $t=0$ is due to the previous equilibration and
    temperature rap. (b) Calculated thermal conductance for C4-C10 using
    temperature gradients of $\Delta T=20,40$~K. For each molecule and
    temperature gradient, data from three different MD runs is displayed. For
    C6 at $\Delta T=40$~K two points fall together onto the the low thermal
    conductance value of around 18~pW/K.}
  \label{fig-AlkaneNEMD}
\end{figure}

To close the analysis, we study temperature-induced geometry changes of
single-molecule junctions and their effect on the thermal conductance using
NEMD simulations. The chosen interatomic interaction potentials are a crucial
point and need to describe reliably the molecular geometry, those of the
metallic electrodes and at the same time the metal-molecule interface. Only in
this way they can reproduce the vibrational modes that determine the phonon
heat transport. As discussed in Sec.~\ref{sec-theory-NEMD}, we construct
junction geometries for the NEMD simulations, see Fig.~\ref{fig-NEMD-Setup},
which show a similar C part as JT1 of Fig.~\ref{fig-ContactGeo}, studied with
the DFT-NEGF approach. We do so to ensure comparability between both
methods. We use the REAXFF of Ref.~\cite{Jaervi2011, Bae2013,Senftle2016} in
our study. It has been optimized for Au-S-C-H systems \cite{Bae2013}, yields
anharmonic interatomic interactions in the whole system, and is able to
describe chemical bond formation and dissociation. Overall, we find it to
yield reasonable junction geometries.

In Fig.~\ref{fig-AlkaneNEMD}(a) the cumulated output of the thermostats is
displayed as a function of simulation time for a C6 junction. As explained in
Sec.~\ref{sec-theory-NEMD}, we calculate the thermal conductance as the slope
of the linear fit, indicated by the red line in Fig.~\ref{fig-AlkaneNEMD}(a),
divided by the applied temperature difference $\Delta T$, see
Eq.~(\ref{eq-kpn-NEMD}). It is visible that the output of the thermostats show
fluctuations on the order of roughly $\pm 5$~eV. Let us note that $\Delta
E^{\text{c}}$ is an extensive quantity that is proportional to the number of
atoms in the regions coupled to the thermostats, and it thus amounts only to
$\pm 8.7$~meV/atom. For each interval of a nanosecond simulation time, we show
a sample geometry as an inset. Interestingly, apart from the extended chain at
the start the alkanes can exhibit different geometrical defects. Temperature
fluctuations in the large atom reservoirs in the L and R regions in
Fig.~\ref{fig-NEMD-Setup} lead to an effective modulation of the electrode
separation in the C part, which can stretch or squeeze the molecule. The
thermal conductance at ambient temperatures arises thus as an average over
geometrical configurations, including chains with and without
defects. Although shown here only for C6, this holds also for the other
molecules.

The thermal conductance for two different temperature differences $\Delta
T=20,40$~K is plotted in Fig.~\ref{fig-AlkaneNEMD}(b) for C4-C10. First of all
we note that there is no significant difference related to the applied
temperature gradient, meaning that we are in the linear-response
regime. Overall the conductances range from 20-40~pW/K. This is somewhat
smaller than the thermal conductance determined for the straight alkane chains
in the different geometries studied in Fig.~\ref{fig-ContactGeo}. In
particular, it is lower than the conductances of JT1, from which the NEMD
geometries are derived and which we predict to lie between 30 and
45~pW/K. Conversely, the results are in good agreement with the values of
$\kappa_{\text{pn}}$, sampled in the pulling curves that started from
defective chains in Sec.~\ref{sec-Alkane-Defects}. For C10 we observe that due
to the mentioned mismatch of interatomic distances between DFT and the REAXFF
at finite temperature, the geometry at one side changes from an atomically
sharp tip to a blunt shape. This corresponds to a higher stress configuration
of the alkane chain, or, in analogy with the DFT studies, to a lower
probability of defect formation. Indeed, $\kappa_{\text{pn}}$ for C10 is
larger than for the other molecules in the NEMD study and in closer agreement
with the DFT results of the straight chain.

Overall, we find a good agreement between DFT-NEGF and NEMD methods for the
thermal conductance. While the results of both approached will depend on the
chosen exchange correlation potential and the selected force field, the
consistency indicates that in these single-molecule nanojunctions, anharmonic
effects are weak. For this reason, vibrations in the C part behave like waves
that proceed elastically through the system at a fixed energy. Since
relaxation of energy and dephasing will happen inside the metal reservoirs,
the phonon heat transport over the nanoconstriction can also be characterized
as phase-coherent.

\section{Conclusions}\label{sec-conclusions}
In this paper, we presented a comprehensive overview of variations in the
phonon thermal conductance of alkane single-molecule junctions at room
temperature. For this purpose, we used different methods: A combination of DFT
and NEGF to study the thermal conductance in the phase-coherent, harmonic
regime and an approach based on classical NEMD to include the effects of
temperature and anharmonicity. Since we have shown in Ref.~\cite{Cui2019} that
the electronic contribution to the thermal conductance plays no role for C4
and longer alkanes, the phonon thermal conductance is equivalent to the full
thermal conductance apart from radiative effects. Due to the particular
measurement scheme, established in Ref.~\cite{Cui2019}, where the molecular
junctions spontaneously break at a fixed electrode separation, radiative
contributions cancel out and the phonon thermal conductance can thus be
uniquely identified.

As the first point, we estimated the variations of $\kappa_{\text{pn}}$ due to
different binding positions of sulfur anchors to the gold electrodes,
including atop, bridge or hollow positions, as well as due to the orientation
of the leads, examining alignments of $(111)$, $(110)$ and $(100)$ crystal
directions with the transport direction. These simulations were done with
extended alkane chains and the DFT-NEGF method. We found the average thermal
conductance to be independent of length within a range of 35-40 pW/K with
variations on the order of $\pm 5$~pW/K. By studying the eigenchannel-resolved
phonon transmission, we could identify peaks originating from similar
molecular vibrations. This served to demonstrate the sensitivity of individual
modes to the precise contact geometry. Next, we looked at the influence of
molecule-internal disorder. For this purpose, we generated a set of junction
geometries, where the alkane contains at least one gauche
defect. Subsequently, we varied the distance between the electrodes to
investigate the response of the defects to different strain conditions and the
impact on heat flow. Consistently, we found in all of the examples that the
defects vanish with increased lead separation. Furthermore, in all cases the
thermal conductance of the defective chain was reduced in comparison to the
defect-free chain. The cumulated conductance revealed that no specific modes
within a particular energy range are responsible for the reduction. By
averaging over the set of geometries in the conductance-distance curve, we
estimated an average $\kappa_{\text{pn}}$ within a range of 20-30
pW/K. Finally, we calculated the room-temperature conductance within the
framework of NEMD. While we did not pull the junction, the use of large
reservoirs of gold atoms in the electrodes led to thermally induced
modulations of the electrode separation. These displacement fluctuations
caused a spontaneous appearance or vanishing of molecule-internal defects
within the simulation time. With the NEMD method we computed a thermal
conductance for C4-C10 in the range of 20-40 pW/K, which is consistent with
the previous DFT-NEGF approach.

We note that our NEMD simulations have important implications for using
molecule-internal disorder to tune the thermal conductance \cite{Li2015}. If
the time to measure the thermal conductance is faster than the transition
between different molecular structures, they will be identified in thermal
conductance measurements. In the opposite limit, the thermal conductance will
appear as an average over structures with straight or defective chains. This
latter case is the experimentally relevant situation, since measurements need
to average over many seconds to reveal a signal \cite{Cui2019}, while our
simulations show that gauche defects appear and vanish on picosecond time
scales. This kind of average due to a low time resolution of measurements was
considered in Ref.~\cite{Li2015} for graphene electrodes, which show a highest
phonon energy of around 185~meV as compared to the 20~meV of Au studied
here. The thermal average over different molecular configurations is expected
to result in a rather continuous mechanical tuning of the phonon heat
transport, and the corresponding increase in thermal conductance due to an
increasingly extended alkane would be overlaid by a weakly decreasing
radiative heat transport contribution with increasing electrode separation for
our three-dimensional metal electrodes \cite{Kloeckner2017a}.

In summary, our study reveals that the thermal conductance of molecular
junctions depends crucially on the strain state and is sensitive to the
precise atomic configuration. While the heat conductance value will depend on
the exchange-correlation functional or force field parametrization used in the
DFT-NEGF and NEMD approaches, the consistency of results is reassuring. It
confirms that anharmonic effects due to phonon-phonon scattering, taken into
account in the NEMD method, do not play a major role in these molecular
junctions containing only short molecules. In this sense we identify phonon
transport to be elastic and phase-coherent. Since the phonon transport through
single-molecule junctions is now experimentally accessible \cite{Cui2019}, we
hope to guide and stimulate future experiments with our study.

\section{Acknowledgments}
J.C.K.\ and F.P.\ thank P.\ Reddy, E.\ Meyhofer, J.\ C.\ Cuevas, D.\ M\"ohrle,
and A. Irmler for inspiring discussions on this project. In addition, both
authors gratefully acknowledge funding from the Carl Zeiss foundation, the
Junior Professorship Program of the Ministry of Science, Research and the Arts
of the state of Baden W\"urttemberg, and the Collaborative Research Center
(SFB) 767 of the German Research Foundation (DFG). An important part of the
numerical modeling was carried out on the computational resources of the bwHPC
program, namely the bwUniCluster and the JUSTUS HPC facility.

redpajama_set_name: RedPajamaArXiv


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"What If" is sonically another winner for Ms. Arie, but it is the message that is ringing even louder and clearer to us. Check out "What If" below and tell us what you think.


text:
Q: Common font on different devices' browsers What is most common font on different desktop and mobile devices. I need my website texts have same look and size on different devices.
Since I need it for Arabic scripts, I can't use web fonts, because Arabic (right to left) web fonts are not rendering properly on all devices, yet.

A: Even the same font will look differently on different devices, especially on mobile devices. The way it looks will be affected but the native rendering of fonts, and also by the default font size relative to the screen dimensions on each device. Finally, users are allowed to adjust font sizes on almost all devices, and they often do - especially on large PC monitors.
The only reliable solution is to use a responsive layout, which displays your content correctly regardless of the font size or content length.


Clth, 7.25 x 9.25 in. / 172 pgs / 156 color.
Edited and with text by Jordan Sullivan.
Shot in Iceland on 35 mm and Polaroid film, The Young Earth is a fictional photo series by New York-based artist Jordan Sullivan that follows two Americans in their twenties, one of them terminally ill, as they explore the idyllic and remote corners of Iceland. There, they are forced to confront their own mortality and a past love triangle that had previously disrupted their friendship. What bonds the two young men in their last days together is fear: one man faces his impending death, the other faces his own uncertain future and the loneliness of the world without his best friend. Through meditations on death, the end of youth and the beauty and complications that come with love and friendship, the narrative examines how we might find courage in the face of oncoming tragedy. The Young Earth is the first volume in Sullivan's Wandering Days book series.
Featured image is reproduced from Jordan Sullivan: The Young Earth.
FORMAT: Clth, 7.25 x 9.25 in. / 172 pgs / 156 color.
Published by Peter Hay Halpert Fine Art.