[gmx-users] eelctric field

[Amin Rouy]

Dear Christian,

Thank you for your reply. However, still it is not fully clear to me. Lets
only talk about gmx energy.  How it happens that I get from gmx energy
similar values of energies (LJ, columbs, total energies) while a different
pressure, with and without applied filed? The total energy should be
different as a result of an additional energy due to applied filed on each
atom.

On Wed, Nov 13, 2019 at 3:10 PM Christian Blau <blau at kth.se> wrote:

> Hello Amin,
>
>
> When you apply an electric field during the simulation by setting the mdp
> parameters like E-x =... as you describe,
> nothing more happens than that each atom experiences an additional force
> that is "atom charge * field strength". The
> energy terms or virial (that then would relate to pressure coupling) are
> not influenced by this. If these terms differ
> between a simulation with electric field and one without, then only
> because the system as a whole responds to the
> applied electric field.
>
> gmx potential on the other hand is an analysis tool that is per se
> unrelated on how you chose to apply an electric field
> during your simulation or not. However, when applying an electric field,
> you would expect a different result from an
> analysis with gmx potential than without electric field, because your
> system will respond to the applied electric field.
>
>
> Best,
>
> Christian
>
> On 11/13/19 2:44 PM, Amin Rouy wrote:
> > Hi,
> >
> > I am using gromacs 5.0.4. I apply a uniform electric field in x direction
> > of my box (no walls),
> > E-x= 1  10  0, and simulation runs without error.
> > I notice that the values of electrostatic interactions I get from the
> > simulation is the same as without the an electric field. Which is
> strange,
> > but according to previous questions in the gromacs forum this is true:
> > ''gmx potential only calculates the electric field and potential of the
> > system. It does not take into account the applied field.''
> >
> > Now, my question is are the other quantities obtaining from gmx energy
> take
> > into account field effect? e.g. pressure of the system.
> --
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