[gmx-users] Coulombic potential modifiers in Gromacs 4.6.4.

[Mark Abraham]

On Nov 21, 2013 9:20 AM, "rajat desikan" <rajatdesikan at gmail.com> wrote:
>
> Hi All,
>
> I was wondering about the coulomb-modifier = Potential-shift-Verlet option
> in conjunction with the Verlet cut-off scheme and PME.
>
> I can understand that vdw-modifier = Potential-shift-Verlet shifts the
> truncated LJ tail by a constant so that the potential is the integral of
> the force.

No, see http://manual.gromacs.org/online/mdp_opt.html#el. The whole
potential is shifted by the value that it would otherwise have had at the
cut-off. This is cosmetic in MD, unless you plan to compute based upon the
energies. Whether something else is trying to compensate for the missing
long-range interactions has nothing to do with it.

Mark

>  What does the coulomb-modifier do? We are accounting for the
> long range coulombic interactions using reciprocal space sums in PME,
> right? What exactly is the shift here?
>
> Thanks
>
> --
> Rajat Desikan (Ph.D Scholar)
> Prof. K. Ganapathy Ayappa's Lab (no 13),
> Dept. of Chemical Engineering,
> Indian Institute of Science, Bangalore
> --
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