[gmx-users] David, a question about your shell water model.

xieyh at hkusua.hku.hk xieyh at hkusua.hku.hk
Tue Apr 26 11:38:28 CEST 2005

Dear Dr. David:

In my system, I applied an uniformly external electrical field across the box.

1. Here, is external field mainly from the applied electrical field?

2. You said: "There are no intramolecular interactions as you can see from the
topology file"

I don't understand this sentence. Shell particle and oxygen/hydrogen atoms are
all charged. Why no electrostatic interactions among them? Because it is a
shell atom, and no Coulomb interactions exist between shell and other atoms?

3. The dipole moment is a result due to the electric field.

This is just my question, here, the electric field you meant is only external
field from intermolecular interactions (because no intramolecular interactions
in your model). But normally, the electrical field should include both external
and internal field, is it right?

By the way, in my model, it is difficult to minimize the position of shell every
step. So, I give a small mass to shell particle, and make MD in normal way. In
this case,

4. Whether the electrostatic interactions between shell and surrounding atoms
should be considered?

5. The dipole moment should be contributed from both the applied external field
and the local field generated from shell and surrounding atoms?

I felt very sorry to give you so many questions. But, I am the first time to use
GMX to consider a shell model, many things are still confused to me. I believe
you can give me great help.

Thanks a lot.

Xie Yinghong
Hong Kong Univ. 

> >Dear David:
> >
> >After reading your paper "Molecular Dynamics Simulations of water with Novel
> >Shell-Model potentials", I am a little not sure about the following thing. 
> >
> >To a shell particle, a balance of force can be written as: k.r=q.E. 
> However,is
> >the electric field E the summation of external and internal field? If yes,
>in a
> >box of water, does the interal field also play an important role in e.g.
> >deciding the dipole moment?
>External field is due to intermolecular interactions. There are no
>intramolecular interactions as you can see from the topology file. The
>dipole moment is a result due to the electric field.
> >Thanks.
> Xie Yinghong
> Hong Kong Univ.

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