[gmx-users] Dimensionless units question

Amit Choubey kgp.amit at gmail.com
Fri Jul 29 19:24:40 CEST 2011


reduced units works for LJ particles only. I am not sure if it works when
you include electrostatics. When you set charge = 1 it is 1electronic
charge. I would suggest not to use the reduced units for LJ in this


On Fri, Jul 29, 2011 at 8:05 AM, Alex Marshall <amarsh59 at uwo.ca> wrote:

> 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?
> Thanks,
> Alex
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