[gmx-users] Dimensionless units question

[Alex Marshall]

Hi Amit,

So if I understand you correctly, any LJ interaction I impose on these
particles will be quite arbitrary because I'm only concerned with
electrostatics, right? How then might I go about comparing the dimensionless
reference values given with the values I calculated? I don't think I can
simply compare their ratios, as there would still be a unit of length to
deal with.

Thanks,
Alex

On Fri, Jul 29, 2011 at 2:24 PM, Amit Choubey <kgp.amit at gmail.com> wrote:

> Hi,
>
> 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
> scenario.
>
> Amit
>
> 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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>
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