[CPMD-list] GROMACS/CPMD with ESP

[Axel Kohlmeyer]

christian,

On 1/18/08, Christian Seifert <cseifert at bph.ruhr-uni-bochum.de> wrote:
> Hi.
>
> I need the ESP charges of the QM Atoms of a GROMACS/CPMD simulation, but it is

please explain how you come to this conclusion.

> only available for EGO(=IFTYPE.EQ.1). See: line 916 of egointer.F
> (version:CPMD-3.11.1):
> IF(TEXTFLD.AND.IFTYPE.EQ.1) THEN
> ...
> [ESP]
> ...
> ENDIF
>
> May I just edit the IF command or would that induce failures in the
> calculation?

i would suspect that you will have a double counting of the
electrostatic interactions of the QM atoms with the MM atoms.
but of course, the best way to get an answer is to pick a simple
enough input example and compare all-QM with all-MM and QM/MM
and see if the forces are reasonable.

> GROMACS reads the charges from the qmoutput.out, but if they are always zero,
> there would be no sense.

have you had a look at the subroutine GMX_EL_FORCES() also in egointer.F?
from the looks of it and because i know that the gromacs qm/mm interface
uses a much more sophisticated approach than the ego interface, i would
guess that the force contributions that would be otherwise computed from
the ESP charges are directly computed within CPMD.

i have cc'd pradip who is the expert for this part of the code
and should know for sure.

cheers,
   axel.

>
> Greets,
> Christian.
>
> --
> B. Sc. Christian Seifert
> Department of Biophysics
> University of Bochum
> ND 04/67
> 44780 Bochum
> Germany
> Tel: +49 (0)234 32 28363
> Fax: +49 (0)234 32 14626
> E-Mail: cseifert at bph.rub.de
> Web: http://www.bph.rub.de
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>


-- 
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Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
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