[gmx-users] Dimensionless units question

Alex Marshall amarsh59 at uwo.ca
Fri Jul 29 17:05:13 CEST 2011

Hi all,

I'm trying to calculate the force on one particle and the total
electrostatic energy of my system, which consists of a lattice of 25 evenly
spaced charges in the xy plane and a single charge in the center above to
preserve charge neutrality. The reference values I have been given are in
dimensionless units, so I am tasked with either converting my output to
dimensionless units or having gromacs work in reduced units from the get go.
I have set the mass of each charge to 1, the magnitude of the charge on each
particle to 1, and the values of the C6 and C12 parameters in my itp file to
4.0, since I'm just using gmx.ff for this (hopefully simple) calculation.
I've turned off temperature coupling because this is purely a test of the
handling of electrostatics with 3D Ewald summation plus the correction for
slab geometry. However, the force and energy I calculate are still quite far
from the reference values. Have I missed anything if I want my output to be
in dimensionless units?

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