Hello Ekatherina, I did not reach a point in my simulations where I have
used freeze command, but I think for your case, can't you put a position
constraint on your quartz layer. In that case, you just have to create an
index file having quartz in the group and then you can put postion
restraints on them in x,y,z by putting force constant of [1000 1000 1000]
so that the layer doesn't move.

Regards,
Debashish





On Thu, 7 May 2020, 10:28 Ekatherina O, <o...@isc-ras.ru> wrote:

> Hello Dr. Dallas Warren,
> Thank you for the suggestions.
>
> But this does not solve the problem of the movement of atoms of quartz
> layers (upper and lower) located at the borders of the box. I would like
> the quartz layers to remain intact during the modeling process, i.e.
> atoms did not move and the initial structure was disturbed. How can I
> solve this problem?
> Can I freeze structure (atoms)? Since with a further increase in
> simulation time, I observe the movement of quartz layers in the box. I
> don’t need them to move.
>
> > Message: 4
> > Date: Tue, 5 May 2020 09:12:51 +1000
> > From: Dallas Warren <dallas.war...@monash.edu>
> > To: GROMACS users <gmx-us...@gromacs.org>
> > Subject: Re: [gmx-users] Need help creating md.mdp for silica(quartz)?
> > Message-ID:
> >       <CAOv1qzY3iYKVgOTJRb=_
> dtxkx86ohdbsdyjg2ma2+tpa8ge...@mail.gmail.com>
> > Content-Type: text/plain; charset="UTF-8"
> >
> > 1/ it means that between the original coordinate file loaded with vmd
> > and
> > the frame you are looking at there from the trajectory file, those
> > atoms
> > have moved across the periodic boundary and vmd is still drawing the
> > bond
> > between them. vmd knows nothing about bonds, it guesses where the bonds
> > should be and maintains them between those atoms when viewing a
> > trajectory.
> > If looking to make a nice looking animation simply using gmx trjconv to
> > move the layer into the center of the box. Otherwise use a viewing
> > method
> > in vmd that doesn't draw the bonds i.e. VDW, Points or one that redraws
> > each frame i.e. DynamicBonds
> >
> > 2/ where the simulation box is located is entirely arbitrary. So if it
> > is
> > not in the location you want then use gmx trjconv to move it to where
> > you
> > want it to be.
> >
> > All these things you are seeing here are artifacts of the periodic
> > boundary
> > condition:
> >
> http://manual.gromacs.org/documentation/current/user-guide/terminology.html#gmx-pbc
> >
> >
> > Catch ya,
> >
> > Dr. Dallas Warren
> > Drug Delivery, Disposition and Dynamics
> > Monash Institute of Pharmaceutical Sciences, Monash University
> > 381 Royal Parade, Parkville VIC 3052
> > dallas.war...@monash.edu
> > ---------------------------------
> > When the only tool you own is a hammer, every problem begins to
> > resemble a
> > nail.
>
> --
> Yours sincerely,
> Ekatherina O.
> o...@isc-ras.ru
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