[gmx-users] Error in comparison of Coulomb-14 potential?

[Mark Abraham]

Hi,

That could be evidence of a bug. If you can upload your grompp inputs, tpr
and log files to a new issue on redmine.gromacs.org we can consider further.

Cheers,

Mark

On Mon, 25 Jan 2016 15:27 Andreas Mecklenfeld <
a.mecklenfeld at tu-braunschweig.de> wrote:

> Dear all,
>
> I want to perform an alchemical change of state of a molecule in TIP3P,
> where I do only change the partial charges of the atomtypes. To control
> my results, I perform two MD runs with the different charge sets
> respectively.
>
> I'm interested in the Coulomb-14 interactions of the solute (since TIP3P
> has none obviously) and would have expected that the potentials of the
> end states match those of the classic runs.
>
> For the classic MD, topology A results in -5.74e+02 kJ/mol, while for B
> it's -9.04e+02 kJ/mol which seems reasonable.
> However, the Coulomb-14 potential of alchemical state A (lambda = 0) is
> -5.74e+02 kJ/mol and for state B (lambda = 1)  it's -5.69e+02 kJ/mol.
>
> I would have expected that the topology of the alchemical end state B
> matches topology B of the MD run, since all parameters should be the
> same. The results are the averages given in the log-files.
>
> Are my considerations wrong or could this be a bug in Gromacs?
>
> Thanks,
> Andreas
>
>
> --
> M. Sc. Andreas Mecklenfeld
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>
> Technische Universität Braunschweig
> Institut für Thermodynamik
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> 38106 Braunschweig
> Deutschland / Germany
>
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>
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>
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