[gmx-users] ChelpG charge or MK charge?

Erik Lindahl lindahl at sbc.su.se
Fri Oct 14 23:15:42 CEST 2005


You'll be fine with MK.

Formally OPLS-AA/L is derived with chelpg, but the differences are  
quite small (Gromos96 has empiric charges). If you want to be really  
picky, the most accurate option is to output the electrostatic  
potential on a grid and then use the RESP program for separate  
fitting in two steps, but it's probably not worth it in this case.



On Oct 14, 2005, at 11:49 PM, <jztan at mail.shcnc.ac.cn>  
<jztan at mail.shcnc.ac.cn> wrote:

> Dear gmx-users,
> My ligand contains a Br atom. When I try to use Gaussian with  
> pop=ChelpG
> to calculate the charge, it told me there is no radius for Br, such  
> as the
> followings:
> Breneman(CHELPG) radii used.
> GetVDW: no radius for atom 1 atomic number 35 (this is Br)
> So I can't use ChelpG charge. I also try pop=MK charge, it can  
> work. My
> QUESTION is what's the main difference between them? Which one is  
> better
> for MD simulation using Gromacs? Any reply is prefered. Thank you very
> much!
> Shanshan
> 2005-10-14
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Erik Lindahl  <lindahl at sbc.su.se>
Assistant Professor, Stockholm Bioinformatics Center
Stockholm University, SE 106 91 Stockholm
Phone: +46 8 5537 8564     Fax: +46 8 5537 8214

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