[gmx-users] QMMM free energy

[Robert fiske]

Actually, before submitting my question I checked google and it appears that 
CPMD does allow partial charges, although I'm not sure if it's intended to 
be used the way we want, so I'll ask that instead, but the answer to a CPMD 
thread on partial charges is here:

http://www.cpmd.org/pipermail/cpmd-list/2006-March/003132.html

It's stated that there can be problems with optimization, but with Gromacs, 
CPMD is only used for single point calculations I believe, so I'm not sure 
of the implications partial charges have with that.

If CPMD does allow valid partial charges for the case we're interested in, 
would it be better to discuss the matter directly with Gerrit, instead of on 
the list?

fiske

>From: "Robert fiske" <rfiske_ at hotmail.com>
>Reply-To: Discussion list for GROMACS users <gmx-users at gromacs.org>
>To: gmx-users at gromacs.org
>Subject: Re: [gmx-users] QMMM free energy
>Date: Wed, 30 May 2007 13:01:28 -0400
>
>
>>Maybe I misunderstand you, but quantum programs are not likely to work 
>>with fractional charges. If you do the charge change in the MM part it may 
>>be possible (but it is definitely not implemented)
>
>I did some tests with CPMD and it appeared to work with fractional charges, 
>I took a simple water molecule and ran a series of calculations changing 
>the charge input from -1 to +1 by increments of .2, I then had someone look 
>at the esp values CPMD gave me for each run and he felt that the results 
>looked correct.  However, I'll send an email to the CPMD list to see if 
>this was just coincidence or if it is indeed implemented in their code.  
>From what I remember the CPMD code does use a floating point variable to 
>hold the charge data, although they may have other reasons for doing so.
>
>fiske
>
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