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

Samuel Silva Pita samuelspita at ibest.com.br
Fri May 25 19:09:32 CEST 2007

 Hi GMX'ers- specially Mark Abraham, 
At the GROMACS compiled with MOPAC 7.0, I tried to simulate my drug, using 
the QM/MM, at two *.itp files: 
(a) At the first I put the CHELPG charge fitting. 
(b) At the second itp file, I put zero charge since all the quantical or 
semi-empirical methods compute the charge calculate (in principle, the 
pontual charge at the quantical method is not necessary) 
When I did the rdf calculate (i.e: (polar oxigen of my drug)-(water 
oxigen))as expected in (a) we have the first (reffered to hydrogen bonds), 
the second, three,... solvation layers while in (b) there are no the first 
solvatation . 
The questions are: 
     Is the pontual charge necessary at *.itp file when we have quantical 
atoms- exactly knowing that quantical method, compute the charges? 
   How "hybrid GMX" interprets the atomic charges? Does GMX calculate the 
atomic charges or we nedded to put it "by our hand"? 
 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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