[gmx-users] qm mm and charges in GMX!

Mark Abraham Mark.Abraham at anu.edu.au
Fri May 25 04:24:33 CEST 2007

Samuel Silva Pita wrote:
> Hi GMX'ers, 
> i've been reading some publications about QM MM calculatiosn intending to 
> aplly this in my system. Since I'd read the GMX Manual and I have some 
> doubts about this recent implemetationat the program. 
>  I'd compile the gromacs with MOPAC 2007 and when I tried to simulate at 
> hybrid level my system: a polar drug and water. I noted interestingly 
> differences at the results. When I applied the CHELPG charges at my drug the 
> QM MM modules correspond to the intended, e.g, the g_rdf has not better than 
> using mechanical simulations(it's obviously!). So I tried to use "0" charges 
> in my drug and the results were identical to when I simulate the benzene 
> (non-polar molecule) in water. 

Please organise your description better. I can't tell what "0" charges 
refer to... why do you have a polar drug and a non-polar molecule which 
is benzene?

>  So I think that GMX does not do QM MM calculations since the program "read" 
> the charges at topology archives (*.itp) and this "dependency" complicate 
> the results. Someone can help me? How can I solve this problem? 
> Kind regards, 
> Samuel Pita. 
> "Do not wear yourself out to get rich;do not trust your own cleverness.  
> Cast but a glance at riches, and they are gone, for they will surely sprout 
> wings and fly off to the sky like an eagle."(Proverbs 23:4-5) 
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