[gmx-users] langevin dynamics

[Berk Hess]

>From: "Syma Khalid" <syma.khalid at bioch.ox.ac.uk>
>Reply-To: syma.khalid at bioch.ox.ac.uk,Discussion list for GROMACS users 
><gmx-users at gromacs.org>
>To: "'Discussion list for GROMACS users'" <gmx-users at gromacs.org>
>Subject: [gmx-users] langevin dynamics
>Date: Tue, 30 Oct 2007 16:55:59 -0000
>
>Dear all,
>
>
>
>I was wondering if someone could offer some advice?
>
>I would like to run an atomistic langevin dynamics simulation (as I don't
>want to include water explicitly). If I add the appropriate langevin
>dynamics options in the mdp file, then is there any reason why I shouldn't
>use explicit counter ions (unfortunately my protein has an overall charge)?
>
>
>
>Obviously I would use periodic boundary conditions so the ions don't wander
>off.

This question has come up many times on the mailing list
and I have answered in many times.
I will answer it once again.

Langevin dynamics is not a magic option that replaces your solvent.
Langevin dynamics only influences the dynamics, not the distributions.
If you choose a high friction, it might mimick the friction of water,
but it does nothing to your potentials.
Therefore you can not use Langevin dynamics will a normal protein
force field and just leave out the water. This will produce a vacuum
simulation.

Berk.

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