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" <[EMAIL PROTECTED]>
Reply-To: Discussion list for GROMACS users <[email protected]>
To: [email protected]
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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