[gmx-users] Re: charges

[quantix1 at gmx.de]

Gamess-US is a quantum package free of charge which can be used to
calculate atomic charges from the ESP (e.g. CHELPG). The source code
is distributed by the Gordon research group at Iowa State University.

http://www.msg.ameslab.gov/GAMESS/GAMESS.html

It is a very nice and powerfull program. Of course it takes a little
learning effort to make it compute what you want. I am quite
proficient in using it. If there is interest, I could spread the 
input decks with the options set to calculate e.g. CHELPG charges.

Uwe

> Graham Smith wrote:
> 
> >Sometimes I have altered the charges by hand using, for example, the
> >differences between compounds containing corresponding charged and
> >neutral groups in the force-field files. 
> >
> >I suppose the best thing would be to do a QM calculation, I think
> >there are quite a few packages available.  
> >
> >I don't know very much about using any of them myself, but they
> >probably have their own user groups: 
> >
> >Widely used, but expensive: 
> >Gaussian: www.gaussian.com
> >Jaguar: www.schrodinger.com
> >
> 
> Personally, I prefer gaussian since we have it available on one of the 
> supercomputing centers where I have an account. This way I don't have to 
> worry about licensing or installing updated versions. But of course it 
> would be nice if somebody has experience of a good free package!
> 
> The nice thing with gaussian is that newer versions allow you to just 
> enter a set cartesian coordinates and the number of electrons for each 
> atom, and then it can either optimize the structure or just derive 
> partial charges (e.g. with CHELPG).
> 
> You can of course optimize things by using symmetries, etc, but this way 
> I could calculate partial charges for the entire headgroup of 64 
> different DPPC lipid conformations (about 35-40 atoms) in a couple of
> days.
> 
> Cheers,
> 
> Erik
> 
> 
> 
> 
> 
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