[gmx-users] Hard Spheres

[Berk Hess]

> Subject: Re: [gmx-users] Hard Spheres
> From: sascha.hempel at bci.tu-dortmund.de
> To: gmx-users at gromacs.org
> Date: Thu, 9 Dec 2010 08:56:54 +0100
> 
> > On Wed, Dec 8, 2010 at 4:01 AM, Sascha Hempel
> > <sascha.hempel at bci.tu-dortmund.de> wrote:
> >         Hi all!
> >         
> >         I am trying to add some hard spheres to my simulation. As far
> >         as i can
> >         tell from the manual Gromacs supports only LJ or Buckingham
> >         for
> >         non-bonded interaction.
> > 
> > 
> > Why cant you use  LJ? By setting the attractive part equal to zero.
> >  
> The LJ Equation is 4 * eps * ( (sig/r)**12 - (sig/r)**6).
> If I either set sigma or epsilon to zero the Potential will become zero
> for all r

Search in the manual for combination rule 1, then you can set C6 and C12.
Also I just replied a week ago to a mail where a user wanted to set C6
to zero while supplying sigma and epsilon, you can do that by putting
a minus sign in front of the sigma.

Another option is using tabulated potentials (user), then you can use anything,
except for completely hard spheres, which would lead to infinite forces.

Berk

> >         
> >         Is there a way to add hard spheres to lets say a simulation of
> >         Water
> >         molecules without interfering into the regular water-water
> >         interaction?
> >         
> >         Thanks a lot in advance,
> >         
> >         Sascha
> >         
> >         TU Dortmund
> >         Laboratory of Thermodynamics
> >         --
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> 
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