text:
\section{Introduction}
Controlled architectures of photo-responsive chromophores can be obtained in an elegant way by self-assembly of functionalized molecules in ordered monolayers.
In this way, photo-switching materials can be potentially exploited in view of realistic applications. \cite{brow-feri06natn,balz+08chpch,russ-hech10am,fuen+11ns,tege12jpcm,aben+15nano}
Azobenzene-functionalized self-assembled monolayers (SAMs) of alkyl chains have been successfully synthesized in the last two decades. \cite{wolf+95jpc,zhan+97cpl,yasu+03jacs,delo+05lang,kuma+08nl,klaj10pac}
Unfortunately, such systems come with a substantial drawback: The photo-isomerization rate is drastically suppressed due to steric hindrance or excitonic coupling. \cite{gahl+10jacs,vall+13lang}
A number of experimental strategies have been suggested to overcome this problem, such as replacing the aliphatic linker by an aromatic one \cite{pace+07pnas} or even bulkier groups, \cite{jung+10lang,jung+12jpcc,jaco+14pccp} or diluting the azobenzene moieties in densely-packed alkanethiolate SAMs. \cite{vall+13lang,evan+98lang,naga+09jesrp,mold+15lang,mold+16lang}

From a theoretical viewpoint the issue of hindered photo-isomerization in densely-packed azobenzene-functionalized SAMs has been addressed by a few works, mainly focused on the excitonic coupling between the chromophores, \cite{utec+11pccp,bena-corn13jpcc} as well as on the effects of a metal substrate. \cite{bena-corn14jpcc}
While these investigations have significantly contributed to describe the excited-state properties of azobenzene derivatives, a very recent publication elucidates the role of defects in the photo-isomerization of such SAMs. \cite{cant+16jpcl}
Still, a full understanding of the fundamental physical mechanisms ruling optical absorption at increasing molecular concentration is still missing.
Identifying the nature of the excitations is an essential step in view of defining new strategies that enable to restore the photo-switching efficiency exhibited by azobenzene in solution.
For this purpose, we provide here an in-depth analysis of the basic physical mechanisms governing photo-absorption in well-ordered azobenzene-functionalized SAMs at increasing packing density of the chromophores.
To do so, we combine \textit{ab initio} many-body theory with differential reflectance spectroscopy.
We investigate the effects of increasing molecular density on the photo-absorption properties of these systems, specifically focusing on the role of intermolecular coupling and local-field effects.
The analysis of the spectra is supported by a detailed characterization of the optical excitations, in view of explaining how many-body effects rule the excitation process.
Good agreement between theory and experiment corroborates our conclusions.

\section{Self-assembled monolayers of azobenzene-functionalized alkanethiols}
\label{sec:systems}
\begin{figure
\centering
\includegraphics[width=.48\textwidth]{H-az.pdf}%
\caption{(Color online) a) Sketch of the experimentally investigated azobenzene-functionalized SAM of alkanethiols on a gold surface. b) Ball-and-stick representation of an azobenzene molecule with \ce{OCH3} termination. Unit cell adopted in the first-principles calculations to model c)
a packed azobenzene-functionalized SAM (p-SAM) and d) its diluted counterpart (d-SAM).
}
\label{fig:H-az}
\end{figure}
In this work, we focus on azobenzene-functionalized alkanethiolate SAMs, which form well-ordered, densely-packed structures with the \textit{trans}-configuration representing the ground state.
Intermolecular interactions in such systems result in a predominantly upright orientation of the alkyl chains as well as of the chromophore (see Fig.~\ref{fig:H-az}a).
On average, the plane of the azobenzene moiety is tilted by 73$^{\circ}$ with respect to the surface. \cite{gahl+10jacs}
The lateral SAM structure has been investigated by atomic-force microscopy (AFM) and scanning tunneling microscopy (STM). \cite{jasc+96jpc,mann+02jpcb}
Densely-packed azobenzene-alkanethiolate SAMs form a nearly rectangular two-dimensional structure with lattice constants $a$=6.05\,\AA{} and $b$=7.80\,\AA{} including two molecules in the unit cell.
Without sacrifying the overall structure of the SAM, the density of azobenzene moieties can be reduced by mixing functionalized and unfunctionalized alkanethiolates. As a consequence of the weaker interaction between the chromophores photo-isomerization is enabled. Additionally, the azobenzene moieties tend to orient more parallel to the surface. For a dilution up to 20$\%$ of a densely-packed azobenzene SAM the average tilt angle of the aromatic plane is about 45$^{\circ}$. \cite{mold+15lang}

In our first-principles calculations, azobenzene-functionalized SAMs are modeled  by a two-dimensional crystal structure, where the alkyl chains and the gold surface are not considered.
This choice is motivated by the fact that the alkyl chains do not contribute significantly to the optical absorption at photon energies below 6\,eV, and that the azobenzene moieties are expected to be decoupled from the gold substrate by the alkyl chains.
To mimic the chemical environment of the bond to the alkyl chain, we add a methoxy (\ce{OCH3}) group terminating the azobenzene molecules (see Fig.~\ref{fig:H-az}b).
We model a densely-packed SAM (p-SAM) by considering an orthorhombic unit cell \bibnote{For the reciprocal-space representation of an orthorhombic unit cell and the identification of the corresponding high-symmetry points, we refer to the Bilbao Crystallographic Server. \cite{aroy+11bcc}} of lattice parameters $a$ and $b$, incorporating two molecules oriented parallel to each other and tilted by 30$^{\circ}$ with respect to the surface normal corresponding to the $ab$ plane (Fig.~\ref{fig:H-az}c).
In this configuration the chromophores are separated by $\sim$2\,\AA{} and $\sim$3.8\,\AA{} in the direction parallel and perpendicular to the plane of the phenyl rings, respectively.
We include $\sim$14\,\AA{} of vacuum in the normal direction, to avoid unphysical interactions between the replicas.
To model a SAM with reduced packing density, we consider a system including only one molecule per identical unit cell.
In the following, we refer to the structure shown in Fig.~\ref{fig:H-az}d as diluted SAM (d-SAM).
For comparison with the isolated molecule, we study also a single azobenzene chromophore in an orthorhombic supercell, incorporating $\sim$6\,\AA{} of vacuum in each direction.
The electronic and optical properties of the investigated systems depend essentially on intermolecular distances.
Only minor effects are expected to come from the orientation of the molecules in the unit cell and with respect to each other.
For this reason, we can rely on the geometries adopted in our first-principles calculations, although rather simplified compared to the experimental sample.

\section{Theoretical background }

Ground-state properties are obtained in the framework of density-functional theory (DFT), adopting the linearized augmented planewave (LAPW) plus local orbital method as implemented in the \texttt{exciting} code. \cite{gula+14jpcm}
Optical absorption spectra are calculated from many-body perturbation theory, following a two-step procedure: Quasi-particle (QP) energies are evaluated from $G_0W_0$ \cite{hedi65pr,hybe-loui85prl} and optical excitations are computed with the Bethe-Salpeter equation (BSE), an effective equation of motion for the electron-hole ($e$-$h$) two-particle Green's function. \cite{hank-sham80prb,stri88rnc}
This methodology allows for describing optical excitations in molecular materials from the gas-phase to the condensed matter. \cite{hiro+15prb,jacq+15jctc,cocc-drax15prb1,brun+15jcp,ruin+02prl,pusc-ambr02prl,humm+04prl,humm-ambr05prb}
In matrix form, the BSE is expressed as
\begin{equation}
\sum_{v'c'\mathbf{k'}} \hat{H}^{BSE}_{vc\mathbf{k},v'c'\mathbf{k'}} A^{\lambda}_{v'c'\mathbf{k'}} = E^{\lambda} A^{\lambda}_{vc\mathbf{k}} ,
\label{eq:BSE}
\end{equation}
where the indexes $v$ and $c$ indicate valence and conduction states, respectively.
In a spin-unpolarized system the effective two-particle Hamiltonian \cite{rohl-loui00prb,pusc-ambr02prb} reads:
\begin{equation}
\hat{H}^{BSE} = \hat{H}^{diag} + 2 \gamma_x \hat{H}^x + \gamma_c \hat{H}^{dir}.
\label{eq:H_BSE}
\end{equation}
$\hat{H}^{diag}$ is the \textit{diagonal} term, which accounts for single-particle transition energies.
Considering only this term in Eq.~\ref{eq:H_BSE} corresponds to the independent-particle approximation (IPA).
The term $\hat{H}^x$ includes the short-range exchange Coulomb interaction $\bar{v}$, which accounts for local-field effects (LFE):
\begin{equation}
\hat{H}^x = \int d^3\mathbf{r} \int d^3\mathbf{r}' \phi_{v\mathbf{k}} (\mathbf{r}) \phi^*_{c\mathbf{k}} (\mathbf{r}) \bar{v}(\mathbf{r},\mathbf{r}') \phi^*_{v'\mathbf{k}'} (\mathbf{r}') \phi_{c'\mathbf{k}'} (\mathbf{r}'),
\label{eq:Hx}
\end{equation}
where $\phi$ are QP wave-functions.
$\hat{H}^{dir}$ contains the statically screened Coulomb potential $W$, which describes the attractive $e$-$h$ interaction:
\begin{equation}
\hat{H}^{dir} \! \! = \! - \! \! \int \! \! \! d^3\mathbf{r} \! \!  \int \! \! d^3\mathbf{r}' \phi_{v\mathbf{k}} (\mathbf{r}) \phi^*_{c\mathbf{k}} (\mathbf{r}') W(\mathbf{r},\mathbf{r}') \phi^*_{v'\mathbf{k}'} (\mathbf{r}) \phi_{c'\mathbf{k}'} (\mathbf{r}').
\label{eq:Hdir}
\end{equation}
The screened Coulomb potential $W$ is calculated from the inverse of the macroscopic dielectric tensor, evaluated within the random-phase approximation.
Details on the implementation within the LAPW formalism can be found in Refs.~\onlinecite{pusc-ambr02prb,sagm-ambr09pccp}.
The coefficients $\gamma_x$ and $\gamma_c$ in Eq.~\eqref{eq:H_BSE} enable \textit{turning on} and \textit{off} the exchange and the direct term, $\hat{H}^x$ and $\hat{H}^{dir}$ (Eq.~\ref{eq:Hx} and~\ref{eq:Hdir}), respectively.
The solutions of the full Hamiltonian in Eq.~\ref{eq:H_BSE} ($\gamma_x$ = $\gamma_c$ = 1) correspond to \textit{singlet} excitations.
When the $e$-$h$ exchange interaction is neglected ($\gamma_x$ = 0 and $\gamma_c$ = 1) \textit{triplet} solutions are obtained.
Further details on the BSE Hamiltonian and on its spin structure can be found in Refs.~\onlinecite{rohl-loui00prb,pusc-ambr02prb}.
For bound excitons below the QP gap ($E_g$) obtained from $G_0W_0$ binding energies ($E_b$) are computed as the difference between $E_g$ and the excitation energies $E^{\lambda}$.
The eigenvectors $A^{\lambda}$ of Eq.~\ref{eq:H_BSE} provide information about the character and composition of the excitations.
In particular, they are used to define the weight of each transition between valence and conduction states at a given $\mathbf{k}$-point:
\begin{equation}
w^{\lambda}_{v\mathbf{k}} = \sum_c |A^{\lambda}_{vc\mathbf{k}}|^2 , \, \, \, w^{\lambda}_{c\mathbf{k}} = \sum_v |A^{\lambda}_{vc\mathbf{k}}|^2,
\label{eq:w}
\end{equation}
where the sums are performed over the range of occupied and unoccupied states included in the solution of the BSE (Eq.~\ref{eq:H_BSE}).
The eigenvectors $A^{\lambda}$ enter the expression of the oscillator strength, given by the square modulus of
\begin{equation}
\mathbf{t}^{\lambda}= \sum_{vc\mathbf{k}} A^{\lambda}_{vc\mathbf{k}} \dfrac{\langle v\mathbf{k}|\widehat{\mathbf{p}}|c\mathbf{k}\rangle}{\varepsilon_{c\mathbf{k}} - \varepsilon_{v\mathbf{k}}} ,
\label{eq:t}
\end{equation}
where $\hat{\mathbf{p}}$ is the momentum operator, and $\varepsilon_{v\mathbf{k}}$ and $\varepsilon_{c\mathbf{k}}$ are the QP energies of the involved valence and conduction states, respectively.
The optical absorption spectra are represented by the imaginary part of the macroscopic dielectric function ($\epsilon_M$)
\begin{equation}
\mathrm{Im}\epsilon_M = \dfrac{8\pi^2}{\Omega} \sum_{\lambda} |\mathbf{t}^{\lambda}|^2 \delta(\omega - E^{\lambda}) ,
\label{eq:ImeM}
\end{equation}
where $\Omega$ is the unit cell volume and $\omega$ is the energy of the incoming photon.
\section{Computational details}
All calculations are performed with the all-electron full-potential code \texttt{exciting}, \cite{gula+14jpcm} implementing the LAPW method.
The ground state of the investigated systems is computed by means of DFT, adopting the Perdew-Wang local-density approximation for the exchange-correlation functional. \cite{perd-wang92prb}
For the sampling of the Brilloiun zone (BZ), we employ a 6$\times$4$\times$1 (3$\times$2$\times$1) $\mathbf{k}$-point mesh for the p-SAM (d-SAM) in both ground-state and many-body perturbation theory calculations.
Concerning the basis functions, a planewave cutoff $G_{max}$=5\,bohr is adopted for the calculation of the single molecule.
For the SAMs, this value is 4.625\,bohr.
Muffin-tin spheres with radii of 0.8\,bohr are considered for hydrogen, 1.1\,bohr for nitrogen, and 1.2 bohr for carbon and oxygen.
Each structure is optimized by minimizing atomic forces within a threshold of 0.025\,eV/\AA{}, with the lattice parameters of the unit cell kept fixed.
The corresponding geometries are displayed in Figs.~\ref{fig:H-az}b-d.

In our $G_0W_0$ implementation, \cite{nabo+16prb} the dynamically screened Coulomb potential $W_0$ is computed within the random-phase approximation.
200 empty Kohn-Sham (KS) states are included in the calculation.
The so-obtained correction of 3.42\,eV, 3.32\,eV, and 1.8\,eV to the band gap of the isolated molecule, the d-SAM, and the p-SAM, respectively, is then applied to the KS electronic structure through a scissors operator.
BSE calculations are performed within the Tamm-Dancoff approximation.
To calculate the screened Coulomb interaction 500 unoccupied states for the molecule and 400 conduction bands for the SAMs are considered.
Approximately 1000 (500) $|\mathbf{G}+\mathbf{q}|$ vectors are included for the d-SAM (p-SAM) and more than 5000 for the single molecule.
In the solution of the BSE Hamiltonian (Eq.~\ref{eq:H_BSE}) for the single molecule we include 16 occupied and 22 unoccupied states, corresponding to about 8 and 5\,eV below and above the Fermi energy, respectively.
In the case of the d-SAMs we consider 11 valence and 15 conduction bands, corresponding to 5 and 4.5\,eV below and above the Fermi energy, respectively.
For the p-SAM, 10 occupied and 11 unoccupied bands are taken into account, corresponding to 3 and 4\,eV below and above the Fermi energy, respectively.

For a quantitative comparison with the experimental data, we calculate optical coefficients, specifically absorbance and reflectance, by adopting the 4$\times$4 matrix formulation of Maxwell's equations, \cite{yeh80ss,pusc-ambr06aem} as implemented in the \texttt{LayerOptics} code. \cite{vorw+16cpc}

\section{Results and Discussion}

\begin{figure*}
\centering
\includegraphics[width=.95\textwidth]{bands.pdf}%
\caption{(Color online) a) Kohn-Sham energy levels of a single azobenzene molecule with the corresponding molecular orbitals; DFT band structures of b) d-SAM and c) p-SAM. The Fermi energy  in the mid gap is set to zero and indicated by a dashed line.
}
\label{figure2_bands}
\end{figure*}

\subsection{Electronic properties}
\label{sec:electronic}
We start our analysis by inspecting the KS electronic properties of the isolated azobenzene and of the SAMs.
In Fig.~\ref{figure2_bands} we show the energy levels of the single molecule, along with the real-space representation of a set of molecular orbitals closest to the Fermi energy.
In the proximity of the KS gap, we find a number of states with pronounced localization on the azo group.
These findings are in agreement with previous studies on \textit{trans}-azobenzene in the gas phase. \cite{crec-roit06jpca,cont+08jacs,maur-reut11jcp}
In particular, the highest occupied molecular orbital, HOMO (H), is distributed almost exclusively on the \ce{N=N} bond, thus being a non-bonding ($n$) orbital.
On the other hand, the H-1 and the lowest unoccupied molecular orbital, LUMO (L) exhibit $\pi$ character with the electron density spread over the phenyl rings.
Further away from the KS gap, the states are localized only on either carbon ring: this is the case of L+1 and L+2, as well as of H-2 and H-4.
These pairs of states are energetically very close to each other.
In between, H-3 is spread over the whole molecule, including the \ce{OCH3} group.
In the conduction region, additional delocalized levels, such as L+3 and L+4, are found at higher energies, more than 3\,eV above the gap.

The electronic properties of the single molecule are reflected also in the SAMs.
By inspecting the band structure of the d-SAM (Fig.~\ref{figure2_bands}b), which includes only one azobenzene in the unit cell, we notice that the KS gap has basically the same size as in the isolated molecule.
The valence-band maximum (VBM) and the conduction-band minimum (CBM) maintain their localized character also in the SAMs.
In the mean-field DFT picture, their energy difference is almost unaffected by the packing arrangement.
Also the very low dispersion of the bands near the fundamental gap confirms the localized molecular character of the electronic states in the d-SAM.
In the valence region, $\sim$2.5\,eV below the Fermi energy ($E_F$), a set of almost flat bands appears.
Again, they are similar to the KS states of the isolated molecule: VBM-2 is rather localized on the \ce{OCH3} group, whereas VBM-3 and VBM-4 are the counterparts of H-2 and H-4, respectively.
The lowest-energy state in this manifold of bands has delocalized $\pi$ character.
Also in the conduction region, we notice strong similarities with the electronic properties of the isolated azobenzene.
About 1.5\,eV above the lowest unoccupied band, we find three flat bands, with CBM+1 and CBM+2 being the counterparts of L+1 and L+2, respectively.
The highest-energy band of this group has instead extended $\pi^*$ character, like the L+3 state in Fig.~\ref{figure2_bands}a.
Below -4\,eV and above 3\,eV, the KS states exhibit a delocalized intermolecular character, as confirmed by the more pronounced dispersion of the corresponding bands.

In Fig.~\ref{figure2_bands}c the band structure of the p-SAM is shown.
Since this system has two molecules per unit cell (Fig.~\ref{fig:H-az}c), bands have double multiplicity.
This is especially evident at the top of the valence region, where the two uppermost nearly dispersionless bands, VBM and VBM-1, have almost the same energy.
They are localized on the azo group and hence exhibit $n$ character like the HOMO in the isolated molecule.
At lower energy in the valence region we find another pair of bands with more pronounced dispersion, namely VBM-2 and VBM-3.
The latter are $\pi$ states, corresponding to H-1 in the single molecule (Fig.~\ref{figure2_bands}a).
Even deeper in energy, about 2\,eV below $E_F$, a manifold of bands appears, including states which are the counterparts of H-2, H-3, and H-4 of the isolated molecule.
In the conduction region, the two lowest-energy bands (CBM and CBM+1) are almost flat and degenerate along the $\Gamma$-X direction, which is almost parallel to the projection of the long molecular axis onto the two-dimensional plane of the SAM (see Fig~\ref{fig:H-az}c).
These states are delocalized over the whole molecule, similar to the LUMO of the isolated compound (Fig.~\ref{figure2_bands}a).
A gap of about 1.5\,eV separates these two lowest unoccupied states from higher-energy ones, which exhibit much more pronounced dispersion.
In this region the KS states show enhanced intermolecular coupling, which results in an increased wave-function delocalization.

\begin{figure}[h!]
\centering
\includegraphics[width=.48\textwidth]{BSE-spectra.pdf}%
\caption{(Color online) Optical spectra of azobenzene molecule and SAMs, expressed by Im$\mathrm{\epsilon_M}$. The $G_0W_0$ gap is marked by a vertical dashed line. a) Singlet excitations, computed from the full BSE. An average over the three Cartesian components is shown for the molecule, while the in-plane ($\parallel$) and out-of-plane ($\perp$) components are plotted for the SAMs. b) BSE spectra, averaged over all Cartesian components, computed without LFE (\textit{triplet} excitations, solid line) and within the independent-particle approximation (IPA, shaded area). A Lorentzian broadening of 0.1\,eV is applied to all the spectra.
}
\label{figure3_BSE-spectra}
\end{figure}

\subsection{Optical properties}
\label{sec:optics}

\begin{table}
\begin{tabular}{c||l|l||l|l||l}
& & \textbf{BSE} & & \textbf{BSE w/o LFE} & \textbf{IPA} \\ \hline \hline
\multirow{4}{*}{\textbf{Molecule}} & \textbf{$S_1$} & 1.25 (\textit{4.09}) & \textbf{$T_1$} & 0.63 (\textit{4.71}) & 5.33   \\
 & \textbf{$S_2$} & 3.87 (\textit{1.47}) & \textbf{$T_2$} & 1.96 (\textit{3.38}) &  5.98 \\
 & \textbf{$S_2$'} & 3.50 (\textit{1.81}) & \textbf{$T_2$'} & 2.89 -- 3.11 (\textit{2.45}) & 6.80  \\
 & \textbf{$S_3$} & 4.93 (\textit{0.41}) & \textbf{$T_3$} & 3.56 -- 3.66 (\textit{1.78}) & 7.70 \\ \hline \hline

\multirow{4}{*}{\textbf{d-SAM}} & \textbf{$S_1$} & 1.29 (\textit{3.91}) & \textbf{$T_1$} & 0.88 (\textit{4.32})   & 5.20 \\
 & \textbf{$S_2$} & 4.45 (\textit{0.76}) & \textbf{$T_2$} & 2.28 (\textit{2.93}) & 5.85 \\
 & \textbf{$S_2$'} & 3.79 (\textit{1.42}) & \textbf{$T_2$'} & 3.24 (\textit{1.97}) &  6.64  \\
 & \textbf{$S_3$} & 5.25 & \textbf{$T_3$} & 4.05 (\textit{1.16}) & 7.58   \\ \hline \hline
\multirow{4}{*}{\textbf{p-SAM}} & \textbf{$S_1$} & 2.27 (\textit{1.03}) & \textbf{$T_1$} & 0.55 (\textit{2.76}) &   \\
 & \textbf{$S_2$} & 3.96 -- 4.01 & \textbf{$T_2$} & 1.72 (\textit{1.59}) &  \\
 & \textbf{$S_2$'} & 4.15 -- 4.30 & \textbf{$T_2$'} & 2.75 (\textit{0.56}) &   \\
 & \textbf{$S_3$} & 4.67 -- 4.70 & \textbf{$T_3$} & 3.54 &   \\ \hline \hline
\end{tabular}
\caption{Excitation energies and binding energies (for bound excitons only, in parenthesis) of the \textit{singlet} (S) and \textit{triplet} (T) excitations marked in the spectra in Fig.~\ref{figure3_BSE-spectra}. In case of more than one excitation contributing to the peak, an energy range is listed. All energies are expressed in eV.}
\label{table1}
\end{table}

In Fig.~\ref{figure3_BSE-spectra}a, the calculated optical spectra of the azobenzene molecule and of the SAMs are shown.
The energies of the main excitations are summarized in Table~\ref{table1}.
We start our analysis from the spectrum of an isolated molecule (Fig.~\ref{figure3_BSE-spectra}a, top panel), which is expressed by Im$\epsilon_M$ averaged over the three Cartesian components.
The lowest-energy excitation, $S_1$, is forbidden by symmetry.
It has $n$-$\pi^*$ character, corresponding to an almost pure transition between the HOMO and the LUMO, as reported in Table~\ref{table2}.
At higher energy, at about 3.9\,eV, a strong peak dominates the spectrum.
This excitation, labeled $S_2$, is responsible for the photo-isomerization of azobenzene, switching from the \textit{trans} to the \textit{cis} conformation. \cite{rau-lued82jacs}
$S_2$ is a bound exciton, with $E_b \sim$1.5\,eV.
It exhibits $\pi$-$\pi^*$ character, being dominated by the H-1$\rightarrow$L transition.
At 3.5\,eV $S_2$' appears as a weak shoulder of $S_2$, given by two almost degenerate excitations from H-2 and H-3 to the LUMO.
The localization of these occupied states on a single phenyl ring (Fig~\ref{figure2_bands}a) explains the low oscillator strength of $S_2$'.
The last bound exciton appearing in the spectrum is $S_3$, which shows a remarkably mixed character with contributions from a number of occupied $\pi$ states to the $\pi^*$ orbitals L+1 and L+2 (see Table~\ref{table2}).
The excitation energies of the molecule considered here are lower by a few hundred meV compared to those reported in the literature for bare \textit{trans}-azobenzene. \cite{catt-pers99pccp,astr+00jacs,flie+03jacs,cont+08jacs,maur-reut11jcp}
This is expected, since the presence of the oxygen-based group terminating the molecule (see Fig.~\ref{fig:H-az}a) is known to cause a red-shift of the $\pi$-$\pi^*$ transitions. \cite{utec+11pccp}
On the other hand, the excitation energy of $S_1$ is underestimated by more than 1.5\,eV compared to results from literature (see, \textit{e.g.}, Ref.~\onlinecite{crec-roit06jpca} and references therein).
This can be ascribed to the starting-point dependence of the $G_0W_0$ step, which becomes particularly severe in case of localized KS states, such as the HOMO of azobenzene.
We expect that a hybrid functional as starting point for the $G_0W_0$ calculation \cite{brun-marq12jctc} or self-consistent $GW$ \cite{maro+12prb} would improve the result.
However, this problem does not affect the nature of the excitations, and therefore it is irrelevant for the essence of the present work.

\begin{table*}
\begin{tabular}{c|c|c|c|c}

  & \textbf{$S_1$} & \textbf{$S_2$} & \textbf{$S_2$'} & \textbf{$S_3$} \\ \hline \hline
 \multirow{4}{*}{\textbf{BSE singlet}} & \multirow{4}{*}{H$\rightarrow$L (98$\%$)} & \multirow{4}{*}{H-1$\rightarrow$L (89$\%$)} & H-3$\rightarrow$L (74$\%$) & H-1$\rightarrow$L+2 (22$\%$) \\
  & & & H-1$\rightarrow$L+2 (12$\%$) & H-3$\rightarrow$L+3 (17$\%$) \\
  & & & & H-1$\rightarrow$L+1 (15$\%$) \\
  & & & & H-3$\rightarrow$L (11$\%$) \\ \hline \hline

  & \textbf{$T_1$} & \textbf{$T_2$} & \textbf{$T_2$'} & \textbf{$T_3$} \\ \hline \hline
\multirow{5}{*}{\textbf{BSE triplet}} & \multirow{5}{*}{H$\rightarrow$L (95$\%$)} & \multirow{5}{*}{H-1$\rightarrow$L (94$\%$)} & H-3$\rightarrow$L (81$\%$) & H-3$\rightarrow$L+2 (79$\%$) \\ \cline{4-5}
 & & & H-4$\rightarrow$L (32$\%$) & H-1$\rightarrow$L+1 (72$\%$) \\
 & & & H-5$\rightarrow$L (41$\%$) & H-5$\rightarrow$L+1 (15$\%$) \\ \cline{4-5}
 & & & & H-4$\rightarrow$L+1 (76$\%$) \\
 & & & & H-2$\rightarrow$L+1 (12$\%$) \\ \hline \hline
\multirow{2}{*}{\textbf{IPA}} & \multirow{2}{*}{H$\rightarrow$L} & \multirow{2}{*}{H-1$\rightarrow$L} & H-3$\rightarrow$L & H-1$\rightarrow$L+1 \\ \cline{4-5}
 & & & H-4$\rightarrow$L & H-1$\rightarrow$L+2 \\ \hline \hline
\end{tabular}
\caption{Composition, in terms of single-particle transitions, of the main excitations of the isolated azobenzene molecule. The weight of each transition is given in brackets, including only contributions larger than 10$\%$. In BSE-\textit{triplet} and IPA the contributions of all active excitations embraced by the peaks are listed.}
\label{table2}
\end{table*}

For the analysis of the absorption spectra of the SAMs, we plot the parallel ($\parallel$) and perpendicular ($\perp$) components of the imaginary part of the macroscopic dielectric function: Im$\epsilon_M^{\parallel}$ represents an average of the $ab$ plane of the unit cell depicted in Fig.~\ref{fig:H-az}c-d, while Im$\epsilon_M^{\perp}$ corresponds to the component along the $c$ axis.
The overall pronounced differences reflect the orientation of the molecules in the SAM.
The spectrum of the d-SAM exhibits strong similarities with the one of the single molecule, starting from the position of the QP gap.
In the lowest energy region, we find the n-$\pi^*$ excitation $S_1$, which is still symmetry-forbidden.
At higher energy ($\sim$4.5\,eV), the strong $\pi$-$\pi^*$ peak $S_2$ appears.
Its excitation energy is blue-shifted by about 0.6\,eV compared to the isolated molecule, as a result of two counteracting effects.
On the one hand, the QP gap, represented by the IPA onset (Table~\ref{table1} and Fig.~\ref{figure3_BSE-spectra}b) decreases by 0.13\,eV in the d-SAM, due to intermolecular coupling.
On the other hand, the exciton binding energy is reduced by almost 0.4\,eV, owing to the enhanced screening and wave-function overlap resulting from the packing of the chromophores in the unit cell.
A similar effect is noticed also for $S_3$, which is unbound, \textit{i.e.}, appears above the QP gap.
Compared to the spectrum of the isolated molecule, the excitation energy of $S_3$ undergoes a blue-shift of more than 0.3\,eV (Table~\ref{table1}).

For a quantitative analysis of the character of these excitations, we display in Fig.~\ref{excitons_d-SAM} the corresponding weights (Eq.~\ref{eq:w}) on top of the KS band structure.
Overall, the excitations of the d-SAM show analogous character to those of the isolated molecule.
$S_1$ is an almost pure transition between the VBM and the CBM, which are the counterparts of the HOMO and the LUMO, respectively.
In the same way, $S_2$ is clearly dominated by the transition from the VBM-1 to the CBM, and $S_2$' by VBM-3 to CBM.
Also in the d-SAM, $S_3$ exhibits a remarkably mixed character, with the most significant contributions coming from  VBM-1 and VBM-3 in the valence region and from the four lowest conduction bands.
The polarization of $S_2$ and $S_3$ along the long molecular axis is further emphasized by the predominance of Im$\epsilon_M^{\perp}$ over Im$\epsilon_M^{\parallel}$ (Fig.~\ref{figure3_BSE-spectra}a).

\begin{figure*}
\centering
\includegraphics[width=.98\textwidth]{excitons_d-SAM.pdf}%
\caption{(Color online) Weights of \textit{singlet} (a) and \textit{triplet} (b) excitations of the d-SAM plotted on top of the Kohn-Sham band structure. The size of the red and blue circles is representative of their magnitude.
}
\label{excitons_d-SAM}
\end{figure*}

The optical spectrum of the p-SAM is completely different from the previous ones.
With increasing packing density of the chromophores and thus enhanced intermolecular interactions, the optical gap, represented by the IPA absorption onset, is significantly reduced to about 3.5\,eV (Table~\ref{table1}).
In addition, two specific features are immediately visible in the spectrum displayed on the bottom panel of Fig.~\ref{figure3_BSE-spectra}a.
First, the lowest-energy excitation $S_1$ is optically active, although weak.
It is still found below the QP gap, with $E_b \approx$~1\,eV.
Second, the sharp peak $S_2$, associated with a bound excitonic state in the spectra of the molecule and of the d-SAM, now appears above the absorption onset of the material in a broad absorption band along with other intense excitations.
This behavior is mainly due to LFE, counteracting the red-shift induced by the band-gap narrowing, as an effect of intermolecular electronic interactions. \cite{hahn+05prl,herm+08prl,herm-schw11prl}
Moreover, contrary to the case of the d-SAM where the out-of-plane component of Im$\epsilon_M$ dominates the spectrum in the considered frequency range, here Im$\epsilon_M^{\parallel}$ and Im$\epsilon_M^{\perp}$ show different spectral weights in specific energy regions.
This is obviously related to the character of the excitations involved.
To gain deeper insight, we again consider the excitation weights plotted on top of the KS band structure (Fig.~\ref{excitons_p-SAM}).
As discussed in Sec.~\ref{sec:electronic}, the presence of two molecules in the unit cell gives rise to two bands at the top of the valence region (VBM and VBM-1) and at the bottom of the conduction region (CBM and CBM+1) having the same character as the HOMO and the LUMO of the isolated molecule.
The first exciton $S_1$ arises from a transition between these occupied and unoccupied states, and is now dipole-allowed, due to symmetry breaking.
The weights are homogeneously distributed within the BZ in both valence and conduction regions revealing the intramolecular character of this excitation.
The $n$-$\pi^*$ nature of $S_1$ explains the predominance of Im$\epsilon_M^{\parallel}$ at the absorption onset (Fig~\ref{figure3_BSE-spectra}a).
Around 3\,eV, where a manifold of excitations with similar character as $S_1$ takes place, the in-plane component of the macroscopic dielectric function dominates over the out-of-plane one.
Excitations with $\pi$-$\pi^*$ character start appearing $\sim$1\,eV above the QP gap, at about 4\,eV, where also the relative intensity of Im$\epsilon_M^{\perp}$ overcomes the one of Im$\epsilon_M^{\parallel}$.
In the spectrum of the p-SAM, we identify $S_2$ as the most intense excitation among a manifold of solutions of the BSE exhibiting rather mixed character.
From Fig.~\ref{excitons_p-SAM}a we notice that the largest weights come from transitions between VBM-5 and VBM-6 to CBM and CBM+1, and non-negligible contributions arise also from transitions from the VBM to higher conduction bands.
The weights are not uniformly distributed throughout the BZ, pointing to an intermolecular character of the excitation.
Excitations with the same mixed character but larger contributions from transitions between VBM-2/VBM-3 to CBM/CBM+1 appear in the same energy window (3.9 -- 4.5\,eV).
However, they display lower oscillator strength than $S_2$.
Also $S_2$' shows a very mixed character, and is dominated by contributions similar to those of $S_2$.
Again, we notice an inhomogeneous distribution of the weights in the BZ, indicating an intermolecular character of the $e$-$h$ wave-function in real space.
Finally, we identify $S_3$, in analogy with the molecule and the d-SAM, as an excitation from VBM-2 and VBM-3 to higher-energy conduction bands, namely CBM+2 and CBM+3.

\begin{figure*}
\centering
\includegraphics[width=.98\textwidth]{excitons_p-SAM.pdf}%
\caption{(Color online) Weights of \textit{singlet} (a) and \textit{triplet} (b) excitations of the p-SAM plotted on top of the Kohn-Sham band structure. The size of the red and blue circles is representative of their magnitude.
}
\label{excitons_p-SAM}
\end{figure*}

The striking differences in the optical absorption properties of the p-SAM compared to its diluted counterpart and the isolated molecule are mainly to be ascribed to intermolecular interactions that act in different ways.
The array of closely-packed molecules gives rise to enhanced screening effects, related to more delocalized $e$-$h$ wave-functions, which exhibit a reduced binding strength.
From the spectra in Fig.~\ref{figure3_BSE-spectra}a and the data reported in Table~\ref{table1}, this trend is very clear.
Considering for example $S_2$, we notice that its binding energy decreases systematically with increasing molecular concentration, up to the p-SAM, where this excitation is found more than 0.5\,eV above the QP gap.
Remarkably, a qualitatively similar behavior is exhibited by the core-level excitations from the nitrogen $K$-edge of azobenzene-functionalized SAMs. \cite{cocc-drax15prb}
In that case, the binding energy of the first bound exciton is reduced by about 2\,eV going from the isolated molecule to the p-SAM.
Another important effect of intermolecular interactions is the redistribution of the spectral weight to higher energies, due to dipole coupling.
This mechanism has been rationalized also for azobenzene dimers from a quantum-chemistry perspective. \cite{utec+11pccp,bena-corn13jpcc}
In the present work we demonstrate that such spectral blue-shift is directly associated to LFE, expressed by the short-range $e$-$h$ exchange interaction (Eq.~\ref{eq:Hx}).

In order to quantitatively determine the role of LFE in the spectra of azobenzene-functionalized SAMs, we now compare Fig.~\ref{figure3_BSE-spectra}a and Fig.~\ref{figure3_BSE-spectra}b.
In the latter, the dielectric function is calculated by neglecting LFE, \textit{i.e.}, by setting $\gamma_{x}$=0 in Eq.~\ref{eq:H_BSE}, thereby turning off the \textit{exchange} interaction.
The solutions of the resulting Hamiltonian are the \textit{triplet} excitations.
Being spin-forbidden, they cannot be probed by an optical-absorption experiment.
However, the comparison between \textit{singlet} and \textit{triplet} spectra helps us explaining the role of local fields and excitonic effects in the optical excitations of these systems.
All spectra in Fig.~\ref{figure3_BSE-spectra}b show the same features, namely the lowest-energy dark excitation $T_1$, the intense peaks $T_2$ and $T_3$, and the weaker $T_2$' in between.
The corresponding excitation energies are obviously red-shifted compared to their \textit{singlet} counterparts (Fig.~\ref{figure3_BSE-spectra}a), due to the missing $e$-$h$ repulsive term.
All the \textit{triplet} excitations exhibit similar relative intensity regardless of the packing density, and likewise their nature remains the same from the isolated monomer to the p-SAM.
Specifically, we inspect the character of the $\pi$-$\pi^*$ transition $T_2$ and compare it with its \textit{singlet} counterpart $S_2$.
When intermolecular interactions are negligible or missing, as in the case of the single molecule, this excitation stems almost completely from H-1$\rightarrow$ L, no matter whether LFE are included or not (Table~\ref{table2}).
In fact, already in the IPA spectrum of the molecule shown in Fig.~\ref{figure3_BSE-spectra}b, a sharp peak appears, given by the $\pi$-$\pi^*$ excitation $T_2$.
Also for the d-SAM we find an intense resonance at the onset of the IPA spectrum.
By comparing the character of $S_2$ and $T_2$ in this system (Fig.~\ref{excitons_d-SAM}), the growing influence of intermolecular interactions is evident.
While $T_2$ is given by a pure VBM-1$\rightarrow$ CBM transition, in $S_2$ we find minor contributions also from deeper (higher) valence (conduction) bands.
Also $S_3$ and $T_3$ exhibit a similar behavior.
While the mixed character of this excitation is enhanced upon inclusion of the Coulomb interaction already in the isolated molecule (Table~\ref{table2}), in the d-SAM we notice that many more interband transitions are involved in the composition of $S_3$ compared to $T_3$.

In case of the p-SAM, intermolecular interactions captured by LFE significantly affect the character of the bright excitations $S_2$, $S_2$', and $S_3$.
In the IPA spectrum, that is shown for comparison, the absorption onset is rather featureless.
In the BSE spectrum computed without accounting for LFE (\textit{triplet} excitations) excitonic peaks are prominent, and resemble in energy and nature those characterizing the spectra of the molecule and of the d-SAM.
$T_2$ is an almost pure transition from VBM-2 and VBM-3 to CBM and CBM+1.
Likewise, $T_2$' shows a predominant contribution from lower-energy valence bands to CBM/CBM+1.
$T_3$ retains its mixed character, already discussed for the molecule and for the d-SAM.
Concerning the excitation energies, we notice a similar behavior as in the \textit{singlet} spectra in Fig.~\ref{figure3_BSE-spectra}a: $T_2$ blue-shifts by more than 0.3\,eV from the molecule to the d-SAM.
It results from narrowing of the QP gap ($\sim$0.1\,eV), due to the increased molecule-molecule electronic interactions, and the enhanced exciton delocalization, which reduces the binding energy by about 0.5\,eV.
When going from the diluted to the packed SAM, the excitations undergo a red-shift by approximately 0.6\,eV.
In this case, the reduction of the QP gap is so large ($\sim$2\,eV) that it overcomes the pronounced decrease of exciton binding energies ($\sim$1.4\,eV, see Table~\ref{table1}).
It is worth noting that these spectral shifts are unrelated to LFE, which are not present in the calculation of \textit{triplet} excitations.
Similar effects, due to the coupling of the electronic wave-functions and to the consequent delocalization of the resulting $e$-$h$ pairs as an effect of the increased intermolecular interactions, have been discussed already in the context of organic crystals. \cite{ruin+02prl,humm+04prl,hahn+05prl}
When the effects of local fields are accounted for, as in the \textit{singlet} spectra, they additionally contribute to an overall blue-shift of the oscillator strength and, most importantly, to its redistribution to higher energies.

At this point, we briefly discuss our results in the context of the existing theoretical literature. \cite{utec+11pccp,bena-corn13jpcc}
In the present work, we investigate optical absorption properties of azobenzene-functionalized SAMs from a solid-state physics perspective.
We treat the ordered SAMs as periodic systems, such that the electronic wave-functions are allowed to spread over the infinitely extended structure.
In this way, the interactions between the chromophores are quantitatively taken into account in the ground state as well as in the excited state.
Moreover, our approach for calculating optical excitations based on the solution of the BSE enables us to consider explicitly the effects of the repulsive exchange and of the attractive direct $e$-$h$ Coulomb interaction, which counteract each other.
From the results of this analysis we assert that the blue-shift experienced by the main absorption peaks in the spectrum of the p-SAM is mainly due to intermolecular coupling.
LFE enhance the mixing of single-particle transitions contributing to the excitations, thereby turning a sharp resonance into a broad absorption band.
The $e$-$h$ pairs become delocalized, assuming intermolecular character.
In this regard, our findings are in line with the rationale expressed by previous theoretical works, \cite{utec+11pccp,bena-corn13jpcc} where SAMs have been modeled in a quantum-chemical framework, accounting for dipole-dipole interactions in molecular dimers and/or clusters.

\subsection{Differential reflectance spectra}
\label{sec:DRS}

\begin{figure*}
\centering
\includegraphics[width=.8\textwidth]{DeltaR.pdf}%
\caption{(Color online) Optical coefficients of the molecule and SAMs from theory (a-c) and experiment (d-f). The differential reflectance spectra of the SAMs with $s$- and $p$-polarized light are obtained under an angle of incidence of 45$^{\circ}$. A Lorentzian broadening of 0.25\,eV and 0.1\,eV is applied to the theoretical spectrum of the molecule (a) and of the SAMs (b,\,c), respectively.
}
\label{DeltaR}
\end{figure*}

To experimentally investigate the effect of increasing density of chromophores on the optical properties of azobenzene-functionalized alkanethiolate SAMs (Fig.~\ref{fig:H-az}a), we use the azo compound 11-(4-(phenyldiazenyl)phenoxy)-undecane-1-thiol (referred to as Az11) synthesized in the group of Rafal Klajn (Weizmann Institute of Science, Revohot, Israel), as well as dodecane-1-thiol (C12, Sigma-Aldrich).
A SAM is prepared by immersing a gold substrate into a methanolic solution of the thiols for 20 hours, as detailed in Ref.~\onlinecite{mold+15lang}.
Depending on the relative concentrations of Az11 and C12 in solution, SAMs with different chromphore densities are obtained.
Since the mixing of the molecules in the SAM is mainly statistical, the local environment of the azobenzene moieties is not homogeneous, in contrast to our first-principles calculations.
The optical properties of the SAM are determined by differential reflectance (DR) spectroscopy,  measuring the reflectance of the gold before and after the SAM preparation.
All measurements are performed at ambient conditions, with an angle of incidence of 45$^{\circ}$, with both $s$- and $p$-polarized light.
Additional experimental details are reported in Ref.~\onlinecite{mold+15lang}.
For a direct comparison between theoretical and experimental data, we calculate DR spectra of azobenzene-functionalized SAMs on gold by employing the \texttt{LayerOptics} code. \cite{vorw+16cpc}
The contribution of the SAMs, assumed to form a 2 nm thick layer, is given by the full dielectric tensors computed from BSE.
The effects of the gold substrate are incorporated in a dielectric constant $\epsilon_{sub} = \epsilon_1 + i\epsilon_2$= -0.36 + $i$6.475.
This value is extracted from the average of the complex refractive index of gold, in the frequency region between 3 and 4.5\,eV, \cite{palik98book} corresponding to the $S_2$ excitation band of the azobenzene-functionalized SAM.
The choice of the dielectric permittivity of the metal substrate is crucial to capture the essential features of the experimental DR spectra.
The angle of incidence is set to 45$^{\circ}$ as in the experiment.
Interference effects at the layer boundaries, as well as the influence of the polarization of the incoming light are taken into account.

In the case of the isolated molecule, absorption measurements are performed in solution.
The resulting absorbance curve is shown in Fig.~\ref{DeltaR}d, while its theoretical counterpart is displayed in Fig.~\ref{DeltaR}a.
Both spectra exhibit the same structure, with an intense peak at lower energy ($S_2$), followed by a weaker one at higher energy ($S_3$).
The first resonance $S_2$ is blue-shifted by approximately 0.3\,eV in the computed absorbance, compared to the experimental result.
This difference can be ascribed to the solvent effects.
The relative intensity of the peaks $S_2$ and $S_3$ is well reproduced by theory, while the absolute energy position of the latter peak is underestimated by about 0.3\,eV.
This behavior can be attributed to the inclusion of the QP correction to the gap, associated to the self-energy of the LUMO, as a scissors operator, that rigidly up-shifts all conduction states by the same amount of energy.
Considering that $S_3$ mostly stems from transitions to states above the LUMO (see Table~\ref{table2}), the application of a scissors operator can be responsible for the underestimation of its excitation energy.
Also the $G_0W_0$ starting-point, as discussed in Sec.~\ref{sec:optics}, can play a role in this regard.

The DR spectra of the packed and diluted SAMs are displayed in Fig.~\ref{DeltaR}\,b,\,c (theory) and Fig.~\ref{DeltaR}\,e,\,f (experiment).
In the first-principles results, the peaks are slightly shifted compared to the maxima in Im$\epsilon_M$ (Fig.~\ref{figure3_BSE-spectra}a).
Specifically, in the case of the d-SAM the first intense peak in Fig.~\ref{DeltaR}b is 0.25\,eV higher in energy with respect to the $S_2$ resonance identified in the macroscopic dielectric function in Fig.~\ref{figure3_BSE-spectra}a.
This difference is not unexpected, since the DR is not only obtained from the imaginary part of $\epsilon_M$, but also depends on its real part.
In agreement with the predominantly upright orientation of the chromophores, the $s$-polarized component is weak in the entire spectral window explored in Fig.~\ref{DeltaR}b, with a single broad peak at the low-energy edge of the $S_3$ band.
For the p-SAM, the energy region between 4.5 and 5.5\,eV is characterized by two peaks associated with $S_2$' ($p$-polarized component only) and $S_3$ (both $s$- and $p$-polarized components) in Im$\epsilon_M$ (Fig.~\ref{figure3_BSE-spectra}a).
At lower energy, around 4\,eV, we identify the spectral features associated with the $S_2$ resonance.
Overall, the $s$-polarized component is enhanced in comparison with its counterpart in the d-SAM.
Between 3 and 4\,eV we notice a weak hump that can be related to a corresponding local maximum in the in-plane component of Im$\epsilon_M$ in Fig.~\ref{figure3_BSE-spectra}a.

The experimental DR spectra of the diluted and densely-packed SAMs (Fig.~\ref{DeltaR}\,e,\,f) are quite similar.
They both exhibit a broad hump in the region of the $S_2$ band of the isolated azobenzene, between approximately 3.2 and 4.5\,eV.
In the case of the d-SAM the maximum in the $p$-polarized component is shifted to higher energies by 0.4\,eV compared to the single molecule, while for the p-SAM this shift increases to 0.65\,eV.
It should be noted, however, that the peak maximum in the DR does not simply correspond to a blue-shifted $S_2$ resonance, but it rather originates from the multitude of excitations appearing in that energy region, as discussed in Sec.~\ref{sec:optics}.
The discrepancy between the measured spectrum of an Az11-SAM diluted with C12 chains and its theoretical counterpart (d-SAM) can be rationalized from the structural difference between the experimental sample and the system modeled from first principles.
While in the latter the orientation of the chromophores is assumed to be the same as in the p-SAM, the diluted SAM sample comprises a mixture of different local molecular environments.
The probability of finding two chromophores on directly neighboring sites is still very high for a dilution to 50$\%$.
Additionally, the chromophores tend to orient themselves more parallel to the surface.
A detailed characterization of the diluted SAM samples is provided in Ref.~\onlinecite{mold+15lang}.
Since the interaction with nearest-neighbors contributes dominantly to the spectral shifts, the experimental DR spectra of diluted and densely-packed SAMs have a similar shape.
Only the energetic position of the peak maximum changes with the chromophore density.

The trends shown by our theoretical and experimental results agree qualitatively, confirming the validity of our analysis and supporting the interpretation of our results.
As demonstrated by the analysis of our BSE spectra, local-fields enhance the effects of the Coulomb screening, giving rise to a significant blue-shift of the oscillator strength.
As such, they play a crucial role in determining the spectral features at large packing density of the chromophores, being responsible for the pronounced mixing of single-particle transitions, which gives rise to the multitude of excitations in the spectral range of interest.
Fine details in the spectra cannot be captured due to the differences between the first-principles description and the experimental setup discussed above.
These differences, however, do not affect the essence of our results.

\section{Summary and Conclusions}
In summary, we have presented a joint theoretical and experimental study on the optical properties of azobenzene-functionalized SAMs.
Our results indicate that at low molecular concentrations the spectra are dominated by an intense $\pi$-$\pi^*$ resonance in the near-UV region, which is known to be involved in the \textit{trans-cis} photo-isomerization of the azobenzene moiety.
At increasing packing density, this resonance is quenched, and the entire spectra undergo a significant redistribution of oscillator strengths to higher energies.
From a thorough analysis based on many-body perturbation theory, we are able to ascribe this behavior to a competition between band-gap narrowing, which tends to red-shift the spectra, and exciton delocalization, which blue-shifts the excitation energies, acting in the same direction as local-field effects.
The latter, in particular, are significantly enhanced by the strong coupling between the chromophores and are responsible for a remarkable mixing of the interband transitions contributing to the main excitations.
While clearly excitonic in nature, excitations become delocalized and the resulting absorption band is significantly broadened.
By lowering the concentration of molecules, the role of intermolecular coupling decreases accordingly, with the optical features of the isolated molecules being restored.

With this analysis we have revealed the fundamental physical mechanisms ruling the photo-absorption properties of azobenzene-functionalized SAMs.
The behavior of these systems upon light absorption is intrinsically dominated by many-body interactions.
This knowledge represents an important step forward in view of understanding and rationalizing the excited-state properties of these complex systems.

\vspace{0.5cm}
Relevant input and output files of first-principles calculations can be found in the NoMaD Repository, with the corresponding DOI: http://dx.doi.org/10.17172/NOMAD/2016.12.07-1.

\section*{Acknowledgement}
This work was funded by the German Research Foundation (DFG), through the Collaborative Research Center SFB 658.
C.C. acknowledges financial support from the \textit{Berliner Chancengleichheitsprogramm} (BCP) and from IRIS Adlershof.
T.M., C.G., and M.W. thank Rafal Klajn and coworkers (Weizmann Institute of Science, Israel) for providing the azobenzene compound.

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Tablets becoming the new classroom computer standard
Posted By Scott Cornell| 08-21-2012
School districts across Canada and the United States have embraced the benefits of tablets.
Schools across Canada and the United States have embraced the benefits of computers. Now, districts are increasingly taking things one step further by turning to tablets.
From April to June of this year, Apple sold 1 million iPads to high schools and universities. This is double the number sold during the same period last year, according to U.S. News and World Report.
"Education tends to be a conservative institution, but we're not seeing that at all on the iPad," Apple CEO Tim Cook said on a July 24 call with investors. "The adoption of the iPad in education is something I've never seen in any technology."
Last year, about 400 school districts in the United States offered students their own iPads, according to a separate U.S. News and World Report article from last September.
"The myth is that textbooks drive what's in classrooms," Jeff Bertrang, principal of Gibbon-Fairfax-Winthrop High School in Minnesota, said to American Public Media. "Textbooks are just resources. The curriculum is what we need to make sure we hit with the kids. We're not focused so much on textbooks as we are on what resources the teachers can find."
In a test conducted in four California school districts last year, students given their own iPad for school work tested at more than 90 percent above the current benchmark. The other students had a 60 percent proficiency. In addition, none of the 76 iPads issued were lost or stolen.
The program at Bertrang's school started in 2010, and he told APM he considered it a success. He said it made kids more engaged in the learning process, and enabled greater collaboration through online portals like wikis.
Orlando Science Schools in Florida will this school year offer iPads to all of its students. Teachers will have to include the devices in their lesson plans, and students need to maintain a certain grade point average in order to keep the tablet for home and school use during the year, U.S. News and World Report said.
"I would say an iPad will one day be the same as a book bag or a ruler or a pencil," Michael Singleton, the head of the charter school's social studies department, said to the publication. "I think that the iPad will be an essential component to schools, [and] it's certainly something we can't ignore as a school – we need to embrace it."
Should schools adopt the iPad as a replacement for a classroom computer? Leave a comment below to let us know what you think!
Scott Cornell
When he's not knee deep in blogging and all things tech, Scott spends his free time playing ultimate Frisbee and watching foreign films. An expert in emerging tech trends, Scott always has his ear to ground for breaking news related to IT security.
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James Franco on his adaptation of 'As I Lay Dying': 'I'm not out to bore anyone'
By Laura Hertzfeld
October 12, 2013 at 02:54 PM EDT
William Faulkner is notoriously hard to read, the bane of many a high school sophomore's existence. But James Franco wasn't one of them. "I've been a huge fan of Faulkner's works since I was in high school and my dad turned me on to his books," Franco tells EW. And many years later, he's now turned As I Lay Dying, Faulker's 1930 tale of a woman who dies and her body is taken to the city to be buried, into a film that uses a split-screen technique to tell the narrative from various characters' points of view. Franco spoke with EW about his experience making the film, his choices in casting — including Eastbound & Down star Danny McBride, and how making comedies with Seth Rogen helped inform his filmmaking , even in creating a serious drama.
ENTERTAINMENT WEEKLY: Why Faulkner?
JAMES FRANCO: As I Lay Dying and The Sound and the Fury were some of the first books I read when I started getting very serious about literature. So at that time it just kind of spoke to me. Even though they were characters living in the early 20th century in Mississippi, for some reason I think I emotionally identified with some of the characters at that time. The other thing I loved and still do love about Faulkner is he created this fictional county and placed most of his best books there; the books are all connected by this fictional place that he created and I love being able to enter an imaginary world that way.
What was the biggest challenge shooting such a complicated book?
It's structurally unconventional. Each chapter is told from the first person perspective of a different character, there are inner monologues that are very dense and use a much higher level of diction than these characters would actually be able to use. So the inner monologues become something more than just an inner voice, it's almost as if Faulkner is giving words to their feelings. These characters wouldn't articulate in the way the monologues do, but maybe they would have feelings as complex as the inner monologues, so Faulkner is giving voice to them.
So I had all these things that would be challenging to adapt but what I like about that challenge is it pushes me to find solutions to the unusual stylistic and structural things in the book.
One of those solutions was the use of the split-screen. Did you try other techniques first? How did you decide that structure would work for this film?
It took us a while to get the rights. I had a long time to think about it and over the course of that time I had certain ideas I was thinking about that I at least wanted to try. So the split screen was one of them. The split screen came from the thing in the book where there are multiple perspectives of a single story. But I didn't want to do it exactly like the book where one chapter goes to one character and then another chapter goes to another character; I felt like if we did it that way it would be a little clunky, a little rigid. I still wanted to get the sense of multiple perspectives, so the split screen idea was something we thought could be a solution but I didn't know if it would work. I'd never done a movie like this before so it was something that we planned before shooting. We shot it in a way that split screen could work but it wasn't until I saw some early edits that I really knew that it could work.
People always say the movie is never as good as the book. What do you think about adaptations in general and are there other book-to-movie adaptation that you looked at for inspiration?
I think of the other kind of saying: 'A good book makes a bad movie and a bad book makes a good movie.' Something like The Godfather — that's kind of a dime-store novel turned into an American classic. Or something like Jaws or The Exorcist, these are all OK books, but the movies are great. I think that the truth to that saying comes from one of the things we love about certain great books: their complexity, the complexity of the prose, the textual complexity that is often very hard to translate into a film because a film is so visual and it can't use ongoing inner monologues or inflected lines of prose in the same way. It needs to use its own terms. Something that can happen often is a movie will capture the narrative or the story of the book but not the style or the structure of a great book. That's why when I chose this book. I was very clear with myself that just adapting the story would not be enough and in fact it's a pretty simple story. But within that are many little mini-narratives with each character. So I said to myself I need some way to capture that in addition to the story, otherwise I'm not truly adapting it. And so I think we did it, I think we achieved it.
I'd never seen Danny McBride in a serious role before. He really pulls off playing it straight here — what was your thought in casting him?
There's not a ton of levity in this movie. And even though Danny isn't playing a comedic role in the movie, I felt like it would just help balance out the weight of the movie if I just had Danny in there. As a filmmaker, what I try to do is take challenging subjects, but I like to make them watchable. I'm not out to bore anybody. So I think having him there was a way to make the movie a tiny bit more fun, even though he's playing a dramatic role and he's great at it. I think it's his first really dramatic movie.
You seem to always be working on a hundred projects at once. How do you get into the headspace to think about such a serious project versus something lighter, like your episodes on The Mindy Project?
I guess for me it's just about engaging with the kind of project it is and gearing my headspace to that project. I've learned by working with some of what I consider the best comedic filmmakers around, mainly Seth Rogan and his team. And just by doing it with them I've gotten used to improvising and figuring out how to find the comedic angles in scenes. In both cases you're telling a story – but in As I Lay Dying when you're looking at a single scene, you're looking to see how is this going to help tell the story and what is the drama that I can mine in each scene? And in a comedy basically you're thinking, well, will this help tell the story and what is the comedy that can be mined in each scene? So they're similar in the sense that you're milking each scene or you're looking at each scene for the comedy potential rather than the dramatic potential. They're kind of similar but you're geared in a different way.
I saw you're working on adapting The Sound and the Fury next. Will there be more Faulkner to come?
We just shot [The Sound and the Fury] in Mississippi and now I'm working with Seth [Rogen] on The Interview. We have a movie about Charles Bukowski's young life that we're hoping to premiere at Sundance.
James Gunn is 'talking' about Brightburn sequel
Laugh-In star Arte Johnson dies at 90
Patrick Swayze to be remembered with new documentary I Am Patrick Swayze
George Clooney to direct, star in 'haunting' post-apocalyptic drama for Netflix
Actor and David Lynch favorite Freddie Jones dies at 91
Official Bond photo shows Daniel Craig working out with leg cast
Viola Davis is making another August Wilson adaptation after Oscar win for Fences
Katherine Heigl to star in and executive produce Netflix adaptation of Firefly Lane
Watch Chris Hemsworth and James Corden compete to be the best waiter
Vanessa Hudgens to lead reading of The Notebook musical adaptation
Scarlett Johansson clarifies recent Rub & Tug remarks were 'widely taken out of context'
Paul Rudd joins new Ghostbusters film: 'I nearly slimed myself!'
Denise Nickerson, Violet in Willy Wonka & the Chocolate Factory, dies at 62
Rip Torn, Larry Sanders Show and Men in Black actor, dies at 88
Watch the first trailer for Rian Johnson's star-studded murder mystery Knives Out
Mortal Kombat movie with James Wan finds its Sub-Zero
Book Adaptations


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Kaspersky develops cybersecurity policy for bionic devices
By Shannon Williams, Mon 6 Dec 2021
Cybersecurity firm Kaspersky is addressing the challenge of the human augmentation phenomenon, by presenting a comprehensive cybersecurity policy.
The document aims to enhance the workforce while also considering employees security and welfare when using bionic devices in the office.
Amid all the excitement and innovation surrounding human augmentation particularly the growing use of bionic devices aiming to replace or augment parts of the human body with an artificial implant there are legitimate fears among cybersecurity experts and the wider community, the company says.
They are concerned that too little attention is paid to the security of the dedicated devices. This lack of awareness around the topic leads to uncertainty and risks for both further development of human augmentation technologies, and a safer digital world in the future.
Kaspersky has been continuously exploring the potential of human augmentation and evaluating security challenges that humanity may encounter during its wider integration into our lives. Following open discussions within the community, the company decided to respond to the specific need for security regulation and designed cybersecurity policy to mitigate security risks that augmentation technology can pose to corporate IT networks.
The document creates a scenario where augmented employees become more common in the company in the future and takes into account Kaspersky's real-life tests with employees' biochip implants.
Developed by Kaspersky security experts, the policy governs procedures for using bionic devices within the company and aims to reduce the associated cybersecurity risks in business processes. The proposed document addresses the entire company's infrastructure and all of its business units. As a result, it applies to the full access control system, as well as administration processes, maintenance processes, and the use of automated systems.
The policy is to be applied to both employees and temporary staff, as well as employees of third-party stakeholders that render contract services to the company. All these factors aim to enhance the cybersecurity of the corporate infrastructure on a larger level.
"Human augmentation is a burgeoning area of technology which in fact remains underexplored," says Marco Preuss, director of Kaspersky's global research & analysis team (GReAT) in Europe.
"That is why making a first step towards clarifying issues related to its use, as well as strengthening security, will help us to ensure its potential is used in a positive way," he says.
"We believe that to build a safer digital world for tomorrow, we need to digitally secure the future of human augmentation today."
The cybersecurity policy initiated by Kaspersky offers a range of standardisation processes, enhancing security and granting better inclusion of employees using bionic devices when in the office.
One of the major objectives of this initiative is also to engage the global IT and augmentation community in the discussion and pursue a collaborative effort for further steps of human augmentation security development. This includes ensuring digital privacy of devices, proving different levels of access rights to stored information, and mitigating any threats related to human health.
Schneider Electric launches comprehensive sustainability framework for data centre operators>>


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Birmingham woman from hard-hit Kentucky city reacts to deadly weekend tornadoes
by: Chloe Vincente, Investigative Reporter/Anchor
Posted: Dec 13, 2021 / 05:52 PM CST / Updated: Dec 14, 2021 / 05:16 AM CST
BIRMINGHAM, Ala. (WIAT) — Denise Reid is counting her blessings after deadly tornadoes tore through where she grew up in Kentucky.
Reid grew up in Bowling Green, Kentucky, but has spent the last three decades in Alabama. Living in the Birmingham area, Reid is no stranger to tornadoes, but said she can't remember ever experiencing the kinds of tornadoes those in Kentucky experienced over the weekend.
"It was part of the reason why it was so horrific," Reid said. "I've lived here in Alabama almost 30 years and we've had some very significant events so knowing what can happen is part of what made it worse for me."
Former FedEx driver dumped hundreds of packages in Blount County because 'he didn't want to deliver them'
Bowling Green is one of the places that was hit the hardest this past weekend. With a rising death toll, as well as many homes and businesses that were destroyed, Reid said she's happy her family there is safe.
"I'd woke up during the night about one o'clock and something just said just check," she said. "You know I've got a lot of family up there and so I picked up my phone and started looking and realized that it was heading toward Bowling Green. There was a tornado, a definite tornado on the ground heading, and in fact the tract was heading towards one of my nieces houses."
Search and rescue efforts continue in Bowling Green. According to CBS News, there were at least 74 confirmed deaths in Kentucky as of Monday.
16-year-old dead after shooting at Northport apartment complex


Employment Agencies in Washington D.C.
List of Washington D.C. permanent and temporary employment agencies, recruitment consultants, staffing firms and headhunters offering support for the employers and provides employment for the job seekers.
The client service I have received through the years has been top notch! I have never hesitated to refer my colleagues to Doyle, since I know that regardless of the nature or length of the assignment Doyle always searches for the best match for their customers. We are celebrating 45 years in staffing!
We specialize in job placement and career advancement for Metro area residents who have struggled to find employment and a community of support. With aid from a host of friends, donors, volunteers and employers-we'll continue to supply work for sustenance, dignity and hope. Donate Make a tax-deductible contribution today! Employ Support Jubilee Jobs by making jobs available.
For the tiny business person who is looking to expand your business, and manage your team effectively, but you do not have the time for details, A+ Staffing Essentials can assist. Let us manage your staff details. We can assist you begin your business or take your business to the next Level. Let the consultants at A+ Staff Essentials guide you as you transition you from the begining-up phase.
Staffing Excellence for over twenty five years! Just 1 block from Metro Center! We're not afraid to announce that we are different from other staffing services. We specialize in working with top notch placement candidates. Only the finest make it into our competitive talent pool because our staffing customer list includes several of Washington DC's most prestigious employers.
In Washington's competitive job market, we know that finding the perfect employee for your organization can be an extremely challenging and rewarding process. In turn, we know that the same challenges and rewards exist for our candidates. Our goal is to provide customers and candidates a perfected placement experience established on personalized service and a dedication to quality.
Whitman Associates. specializes in the search and placement of temp, temp to hire and permanent office support staff. Whitman Associates was set up in 1972 as one of the best permanent placement agencies in the area. Our counselors have achieved the status of Certified Personnel Consultants. Whitman Associates guarantees the highest level of placement.
Set up in 1982, Walton-Thomas International WTI is a specialized staffing service that supplies support to businesses, international organizations, Government agencies, and associations in the Washington, DC metropolitan area. Our main fields of expertise are in the categories of Staffing Services, Bilingual Assistance, and Conference Support.
As industry experts in accounting and finance and information technology recruiting, we provide creative options to suit your unique staffing and employment requirements. Whether you are searching for a temporary or direct hire solution, we welcome the possibility to personally consult with you. Please choose the path that finest defines your area of interest.
Now entering our third decade as a leading force in the metropolitan Washington, DC staffing industry, our team of seasoned specialists are specialists in matching qualified job seekers with a diverse group of customer firms. Both our employees and customers agree that we effectively meet their specific requirements. We hope to add you to that number.
Through the years, we currently have assisted 1000's of people get off the streets, transform their lives, and learn to live independently. You can assist the hungry and homeless this Thanksgiving by joining SOME, Mayor Adrian Fenty and nearly 5,000 SOME supporters at the eighth Annual Thanksgiving Day Trot for Hunger.
I have worked with many DC placement agencies, but Global Excellence far outshines all of them. From day one, Dian was incredibly helpful. She and her staff took the time to stay in touch with me throughout my job search and unusually extensive interview process. The job in which Global Excellence placed me is a dream come true and I couldn't be happier!
Welcome to Banner Staffing., a high-quality supplier of Professional, Management and Administrative support services. Founded in 2000, we currently have experienced steady growth by consistently delivering our customers with reliable, cost-effective solutions. Banner Staffing has been awarded more than fifty contracts using GSA TAPS schedules, 8 a sole source, 8 a competitive, DCSS and commercial contracts.
The Creative Group never ceases to exceed my expectations. The Creative Group, a division of specialized staffing leader Robert Half International., specializes in placing fully qualified creative, advertising, marketing, web and public relations specialists with a range of companies.
PoliTemps supplies quality staff who, in addition to administrative and computer skills, possess an understanding of the political, legislative, and public relations processes in this city. We have the targeting and focus of a public relations company, the aims mission of a staffing service, and the enthusiasm of a political campaign.
About Us We are NRI, a huge diversified staffing services company serving the whole Washington, DC and Baltimore metropolitan areas. We have developed relationships with our employer customers to completely understand their staffing requirements. We have focused on understanding the requirements and challenges of our candidates and temporaries as they seek employment, or to make a change in employment.
On balance, you won't find a better financial and accounting recruiting company than The Leafstone Group. Whether you're searching for a great financial career or need someone with the skills and personality to fit into your financial services department, our recruiters speak your language.
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Jurczenko – Klimczak - Lubniewski: 3 Mini Memoirs
Private Edward Jurczenko
Edward Jurczenko was born to parents Julian and Jozefa (nee Nikolaj) on 3 September 1922 in Stojanow, district of Radziechow, county of Tarnopol (now Ukraine).
While residing there and apprenticing as a locksmith, that part of Poland was occupied by the Soviet Union following the 17 September 1939 invasion and because he was Polish, Edward was deported to the Soviet Union in 1940.
Although Polish prisoners in the Soviet Union were officially released on 30 July 1941, Edward could not enlist in the reborn Polish army until 25 March1942. He was posted to the 28th Infantry Regiment, 10th Infantry Division.
Together with the Polish Army units, he was evacuated to Iran, crossed the Soviet-Iranian border and came under British command effective 1 April 1942. He was transferred to Palestine, via Iraq, arriving on 7 May 1942 where he was posted to the Reserve of the Commander-in-Chief, Polish Army in the Middle East.
On 11 August 1942, Edward was transferred to the Reserve Centre and seconded on a training course to the Army Training Centre on the 17th of that month.
On 3 April 1943 Edward was transferred to the 7th Light Anti-Aircraft Artillery Regiment. He served in the Middle East until the 2nd Corps was shipped to Italy, participating in the Italian Campaign until the end of the war.
The entire 2nd Corps was then transferred to the United Kingdom. Edward arrived in England on 27 July 1946. He enlisted in the Polish Resettlement Corps (PRC) and served in the United Kingdom until his discharge on 20 August 1948, on absorption into industry.
2nd Lieutenant Jozef Klimczak
1st Polish Armoured Division
Fighting in the September Campaign (1939) against the German and Soviet invaders, Jozef Klimczak escaped Poland and rejoined the Polish Army reforming in France.
Following the fall of France in the summer of 1940, Jozef managed to evacuate to Great Britain where he eventually began to train with the Polish 1st Armoured Division, reaching the rank of 2nd Lieutenant and commanding an anti-tank platoon.
The Division served in Normandy within the operational command of 1st Canadian Army (General Crerar), effective August 1, 1944 until May 8, 1945. At various times during the European Campaign, Jozef served alongside troops of the 2nd Canadian Corps (Lt. Gen. Simonds) or the 1st Canadian Corps (Lt. Gen. Crocker).
Jozef was first wounded at Estrees-la-Campagne in France (August 11/44) then for a second time at Noord Bosch, Belgium (October 2/44). Following this second wounding he was flown to the United Kingdom to recover in hospital.
Following his recovery, Jozef attended the London Polytechnic and later, Edinburgh University, following which he began a successful career in his profession.
Antoni Lubniewski
by his son Stefan
My father was born on 29 October 1918 in the village of Malmygi, parish of Kurzeniec, District of Wilejka, and County of Wilno to parents Feliks and Weronika (nee Buter). As a young man he worked on his father's farm while apprenticing as a fitter. He lived through World War Two and settled in England. Antoni managed to save a large number of documents and memorablia from that era.
On 13 April 1940, at 3:00 am in the morning, he was one of eleven family members, parents included, who were forced at gunpoint by the Russian NKVD to abandon the family farm. They were all transported by sleigh to the local railway station where they were loaded into cattle wagons, with up to 40 persons crowded into each wagon. The doors were then shut and they were locked in.
This trainload of Poles was deported to Pawlodar in Kazakhstan. The journey took 18 days and many old people died along the way.
Antoni, his brother, his brother's wife and his sister were then forced to work in the gold mine at Magkain. If you did not work or did not meet your assigned quota, you did not get bread. Many starved to death.
Following the German invasion of the Soviet Union in the summer of 1941, Polish prisoners in the prisons and gulags of the Soviet Empire were officially released on 30 July 1941. Antoni and his brother were among those released and they intended to join the Polish Army being formed on Soviet soil in Buzuluk.
Eventually Antoni was able to get away, leaving the rest of his family behind, marching across Russia for three weeks until he arrived at Panikienda-Ugawoj on 22 March 1942.
He was initially posted to the 1st Anti-Aircraft Artillery Regiment, 10th Infantry Division. The evacuation of Polish units from the Soviet Union had already begun. Antoni's unit crossed into Iran and thereby came under British Command, in Antoni's case, as of 1 April 1942. The unit was then transferred to Palestine, by way of Iraq, arriving there on 29 April 1941. Antoni was posted to the Reserve of the Commander-in-Chief, Polish Army in the Middle East.
With the reorganization of the Polish army, Antoni was transferred to the Workshop Company, 3rd Carpathian Infantry Division effective 18 August 1942. He trained with this unit in Iraq, Palestine and Egypt, before being shipped off to Italy, serving in it until 20 June 1944 when he was reassigned to the Light Aid Detachment (Type A), 6th Lwowska Infantry Brigade, 5th Kresowa Infantry Division.
On 11 December 1944 he was reassigned once more to the 10th Wolynska Rifle Battalion, finishing his war service at the headquarters of the 4th Wolynska Infantry Brigade, 5th Kresowa Infantry Division, with the rank of lance corporal.
He had participated in the entire Italian Campaign and was awarded the Polish Commemorative Monte Cassino Cross and the Bronze Cross of Merit with Swords as well as the British medals, 1939-45 Star, Italy Star, Defence Medal and the 1939-45 War Medal.
Antoni was transferred to England with the Polish 2nd Corps and while resident at the Whitley Camp, Sheffield, was honourably discharged on 4 December 1948.
After going on a training course for the National Coal Board, he worked at the coal face down the Thorseby Colliery at Edwinstowe, Nottinghamshire, until his early death on 23 February 1968 at the age of 49.
Antoni met my mother, Myra Jephson, one of 10 children in a coal mining family, at the Forest Town Miners' Hostel. They married and started a family. I was born in Clipstone Village and went to work down the Clipstone Colliery straight out of secondary school. After 24 years, I am now retired.
One uncle, Edward Matulewicz, married my mother's sister. He had been a sergeant in the Polish 1st Armoured Division. My father's brothers, who were also in the Polish 2nd Corps, did not stay in England. Piotr went back to Poland while Kazimierz emigrated to Argentina.


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This policy "AS-750-12 Resolution on eLearning Policy." was adopted by the Academic Senate May 29, 2012 and supersedes "AS-581-02 Resolution on Distance Education Policy."
eLearning comprises all forms of electronically supported learning and teaching. It is the use of a computer-enabled environment in which students acquire skills and knowledge employing any form of electronic media content delivered on any type of platform.
1) Synchronous Instruction: Instructional activities where both instructor and students are engaging in activities at the same time.
2) Asynchronous Instruction: Instructional activities where the instructor and/or some or all students engage in activities that are not necessarily occurring simultaneously.
1)The degree of computer-mediated faculty/student interaction - Faculty and students can interact face-to-face or in a computer-based virtual space in a scheduled or unscheduled manner. Computer mediated interaction could be mixed (e.g., "hybrid" courses with some traditional classroom lectures supplemented by video conferencing) or it could be complete (e.g., a course in which all faculty /student interaction occurs using a web-based video conference tool).
2) The degree of technology replacement of faculty/student interaction - Technology can have a relatively limited role in course support (e.g., a course uses a small number of pre-recorded video lectures that are posted online) or technology could be used to completely replace faculty/ student interaction (e.g., a web-based, self-paced instructorless course).
Cal Poly has adopted the following definitions of traditional and online instruction.
1) Definition of Traditional instruction courses: these are offered in the traditional mode with an instructor holding class sessions where students are expected to be physically present. Traditional instruction is also synchronous, with both instructor and students engaging in activities simultaneously.
2) Definition of Online instruction: this is instruction delivered via an electronic network such as the Internet.
This policy shall apply to all new and existing credit-bearing courses and programs using eLearning technologies, including online courses and programs offered by Cal Poly. Faculty must submit an eLearning Addendum when proposing to offer new or existing courses online. This addendum can be found in the Propose New Course form and the Edit Course form in the online Curriculum Management system.
Cal Poly faculty have the collective and exclusive responsibility for determining the pedagogies, instructional methods, and best practices most appropriate for the instructional modules, courses, and academic programs.
Whenever a department or faculty group proposes to initiate a degree program in which more than 50% of content is offered online or more than 25 miles off-campus, approval in advance from the Western Association of Schools and Colleges (WASC) is required under the latter's Substantive Change Policy.
An eLearning Addendum to either the Propose New Course form or the Edit Course form must be submitted for curricular review for any new or existing courses in which a total of more than 50% of traditional face-to-face instruction time is being replaced with eLearning technologies.
1) A statement of the degree (in percentage terms) of computer-mediated faculty/student interaction contained in the course (e.g., "30% to 50% of faculty/student interaction for this course is via an interactive web-based video connection").
2) A statement of the degree (in percentage terms) of technology replacement of faculty/student interaction (e.g., "25% of this course is comprised of instructorless self-paced learning modules consisting of web-based video lectures, demonstrations, and automatically-graded quizzes").
Additionally, faculty developing courses that use significant amounts of eLearning technology and faculty participating in curricular review are encouraged to consult the CSU Online Education Whitepaper for a list of assumptions and best practices relevant to the successful development, evaluation, and deployment of online course offerings.


Just fry till the wrapper becomes brown.
Easy right? Really thanks to Food Ink for giving me this awesome sweet date with banana and nutella. ^.^ Really hope there's more to come as I can have more homemade date rather than keep on hunting food date. If lovelies and foodies have story telling or any recipe to share with me, do tell me in comment box below or drop me mail to queenbiifoodie@gmail.com for further chat.
Oooo yummy! Babe I will recommend you trying to use an oven instead of deep frying it!
yummy chocolate and banana!love it.
😭😭 so touching when I knew someone who really learn from my video. Thank you for your great support.
wow!!!I can learn from your post!!!!
looks very simple and easy to make..and yummmsss!!!
banana and nutella is the perfect combination!
Hungry lah... Banana plus chocolate always perfect match.
OMG it looks so good! It's late but now you make me feel like snacking HAhahah!
Your recipe looks so easy to do! Makes me feel hungry when I read your post at night! Nutella and Banana is the perfect combo!
It looks yummy. And, easy to prepare. i should try it too later. by the way, may i know what kind of banana that u use?
Lovely homemade teatime snacks. This look delicious!
Easy and Yummy! Kids would love this for sure. Actually adults too!
looks good.. looks really good! you may just be able to start a business making these!
😊 hope this recipe can made your day..
I saw your creative idea two days ago in your post. i thinking of trying it but no more Nutella at home.
This looks so delicious and so simple to prepare.


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Q: Properties window in design view VSTO I'm new to VSTO and I can't find a way to open property panel for design view. I'm building a VSTO application for the first time

A: You can find Properties Window on the View menu. You can also open it by pressing F4 or by typing Properties in the search box. See Properties window for more information.

redpajama_set_name: RedPajamaStackExchange


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BoardingHouse – USA, 1982
20 June, 2012 5 May, 2019 - Leave a Comment
BoardingHouse – also known as Boarding House, Housegeist and Bad Force – is a 1982 American horror feature film written, directed and starring John Wintergate. It also stars Hank Adly, Kalassu and Alexandra Day.
On September 18, 1972, the Hoffman house was closed due to several mysterious deaths. Ten years later, the house is reopened as a boarding house by a man with telekinetic powers who inherited it. A group of nubile young women quickly move in and the killings begin all over again.
Buy: Amazon.com | Amazon.co.uk
" … we get flying bars of soap, magic shows, ancient synth music, and makeup effects that could have come from Halloween Express. We are warned of bad things to come by the state-of-the-art "Horrorvision" effect – which is a black gloved hand wiggling around in front of a psychedelic background, or sometimes as a blobby silhouette of a ghost" Digital Vault
"Maybe fans of DIY horror will enjoy the garish gore effects, such as a girl envisioning herself with a giant pig's head spurting up blood and a dead mouse, or a doctor in a hospital pulling out his own guts (conveniently located inside his tucked-in shirt). But death scenes, the bread and butter of stupid cheap horror films like these, are too few and far between. One guy is electrocuted in a bathtub, keels over dead in the bathroom, and apparently no-one finds or misses him (!)." DVD Drive-In
"It's VERY hard to believe this nonsense was released to theaters, but it was. I can't explain the strange power Boardinghouse has, but for some strange reason, my eyes never moved from the screen and my mind went into a sort of dreamlike state, where I had no perception on time, rationality, or just the outside world in general. It's that kind of movie." James Oxyer, Obscure Cinema 101
Buy: Amazon.com | Amazon.co.uk | Amazon.ca
Despite being cheaply shot-on-video, the movie was transferred to film and given a limited theatrical release in the United States by Coast Films in 1983.
Code Red released the film on DVD and it was reissued in 2013 by Slasher Video. Cult film fanatic Bruce Holecheck reported: "Remastering the film from its original tapes to fix the problematic dark levels of the previous Code Red release, the disc also features a bonus extended cut that clocks in a full hour longer! I can't even imagine. Other supplements include commentary, interviews, music videos, trailers, galleries… they even have the hilariously obnoxious original "beeping" intro that was on the 35mm print."
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In this episode from the "Louisiana Cooking with a Change of Heart" series of "A Taste of Louisiana" from November 9, 2002, Chef John Folse visits Marjorie Domangue at her home in Gibson, Louisiana, on Bayou Black. She shares her family recipe for Vegetable Beef Soup. In his kitchen, Black Guidry performs his original song, "Cajun Man." Chef Folse then prepares a healthier version of the Vegetable Beef Soup. He also makes healthy versions of Chicken & Artichoke Stew and Peach Cobbler.


#1152 Miniature Bulb Ba15d Base - 12.8 Volt 1.34 Amp 17.152 Watt S-8 Double Contact (DC) Bayonet (Ba15D) Base, 21 MSCP C-6 Filament Design. 500 Average Rated Hours. 2.0" (50.80mm) Maximum Overall Length (M.O.L.), 1.04" (26.5mm) Maximum Outer Diameter (M.O.D.),1.25" (31.80mm) Light Center Length (L.C.L).