From: John Kerrigan (kerrigje_at_umdnj.edu)
Date: Fri Mar 11 2005 - 15:18:48 CST
PBC is essential to simulate the bulk properties of the system (water).
Without PBC, you essentially have a droplet of water in a vacuum, which is
not very realistic. There is more at stake here than just wall or
surface tension effects. PBC is required for using long range
electrostatic methods like PME.
John
John E. Kerrigan, Ph.D.
Academic Computing Services
University of Medicine and Dentistry of New Jersey
On Fri, 11 Mar 2005, Himanshu Khandelia wrote:
> Periodic B.C. are used so that there are no end effects on the wall of the
> simulation. that is about it.
>
> Himanshu Khandelia
>
> Doctoral Candidate,
> Kaznessis Research,
> Department of Chemical Engineering and Materials Science,
> University of Minnesota
>
> Mailing Address:
>
> 499, Walter Library,
> 117, Pleasant St. SE,
> Minneapolis, MN 55455
>
> Phone(o): 612-624-4945
>
> On Fri, 11 Mar 2005, Marc Q. Ma wrote:
>
> > Ed,
> >
> > > There is a physical justification for using PBC, PBC conserve the
> > > momentum of the system. It is my understanding that without PBC
> > > conservation of momentum is violated.
> > >
> > > Ed
> >
> > For conservative systems, conservation of momentum has nothing to do
> > with boundary conditions. For MD as is row, the forces are all pairwise
> > additive, and F12 = -F21. Momentum is strictly conserved. I am not sure
> > about polarizable force fields, I guesstimate it is still true.
> >
> > When there is random force, such as the Langevin Pistons or heat
> > reservoirs, the momentum conservation is going to be violated at each
> > time step.
> >
> > Marc
> >
>
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