[gmx-users] Re: Specific question regarding SPC water model

[Someone Else]

Thanks for the answer.

>You're introducing atomic overlap and thus an energetic singularity from
the infinite Coulombic attraction.
Is there anything I can do  with this?

I posted this question because I'm trying to run a Monte Carlo simulation
of a water box but eventually it finds the global energy minimum (-Inf) and
can't escape from it.


2013/6/4 Justin Lemkul [via GROMACS] <ml-node+s5086n5008760h67 at n6.nabble.com
>

>
>
> On 6/3/13 7:49 PM, tnorgd wrote:
> > Dear group,
> >
> > I am not sure how SPC energy actually works - is there really just one
> VdW
> > interaction - just between two oxygen atoms?
> >
>
> Yep.  A lot of force fields work like that.  Given the size of H atoms
> relative
> to their heavy atom counterparts, the heavy atom to which they are
> connected
> generally governs the vdW interactions.
>
> > If so, when I place a hydrogen atom of one water molecule at the
> location of
> > the oxygen from another water,
> > the two oxygens are separated by the distance of H-O bond length i.e.
> 1.0A.
> > The only VdW interaction is repulsive but finite (and equal ~4E6) but
> the
> > electrostatic between H and O is -Inf = 1/0.0
> >
> > What's wrong?
> >
>
> Nothing.  That makes perfect sense.  You're introducing atomic overlap and
> thus
> an energetic singularity from the infinite Coulombic attraction.
>
> -Justin
>
> --
> ========================================
>
> Justin A. Lemkul, Ph.D.
> Research Scientist
> Department of Biochemistry
> Virginia Tech
> Blacksburg, VA
> jalemkul[at]vt.edu | (540) 231-9080
> http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin
>
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