Failing to optimize geometry of tricalcium bis(phospate) with GAMESS [closed]








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I'm trying to learn how to use GAMESS. I used Avogadro to download the structure of tricalcium bis(phosphate), then I accidentally ran a runtyp=energy on the structure and it succeeded, so I assumed the resulting structure is better than what avogadro got and used that one instead.


I don't even know if geometry optimization is the first thing I should do. Maybe I should use another runtyp first and then optimize the result?


Maybe the fact that it's a salt is what's getting in the way? Maybe I have to specify the charges of the cations and anions somewhere.


Maybe I have to preoptimize it in Avogadro, because I don't think the straight line of 3 Ca followed by 2 $PO\_4$ perfectly aligned remotely resembles what $Ca\_3(PO\_4)\_2$ looks like. (save the pastebin as .log and open it in avogadro so you'll see how it is structured)


Here's a pastebin of the result. The input is printed in the begining, I took off the extended credits section on the begining.


<http://pastebin.com/wivjv9WY>





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> I'm trying to learn how to use GAMESS.
> 
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> I'm not a chemist, my knowledge of chemistry is below amateur level.
> 
> 
> 


There is a serious contradiction out there: quantum chemistry is *way above* amateur level. Unlike playing computer games, quantum chemistry can not be done in a just-get-in-and-drive way. You need a serious theoretical background to make meaningful calculations.


Thus, for instance, you have to understand that usually by default all the calculations in quantum chemical programs are done for an *isolated molecule* in *gas phase*. Doing geometry optimization for ionic compound in such settings is, well, let's say, it is not so meaningful. Very likely, you want to do something totally different, say, establish the crystal structure of solid $\ce{Ca3(PO4)2}$, but that is a totally different task. In fact, you do even need a special program (like [CRYSTAL](http://www.crystal.unito.it/index.php)) to achieve that.


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