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

Samuel Silva Pita samuelspita at ibest.com.br
Fri May 25 01:47:22 CEST 2007

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. 
 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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