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Re: [lammps-users] How to oscillate a wall while thermostatting

# Re: [lammps-users] How to oscillate a wall while thermostatting

 From: Steve Plimpton Date: Wed, 15 Nov 2017 14:20:25 -0700

More generally, you can define a wall consisting
of atoms which move in a prescribed oscillating
manner via fix move.  But make those atoms
be type A atoms which are "invisible" to the fluid.
Then define harmonic bonds between one type B atom
and one type A atom with bond-length 0.0.
B atoms do influence the fluid.
And you can thermostat the B atoms, e.g. via
fix langevin.  The bond strength K will determine
how far the mobile B atoms move from
their associated A sites.

Steve

Steve

On Wed, Nov 1, 2017 at 3:52 AM, Axel Kohlmeyer wrote:
On Wed, Nov 1, 2017 at 5:22 AM, saeed alborzi <alborzi.saeed6@...24...> wrote:
> Thanks for your response.
> I did not get your purpose of asking this question.
> Though, this is variable. You suppose a period of 2 ps and an
> amplitude of 2 angstroms

the purpose of that question is to identify the time scales of the
thermalization and the wall motion. if they differ sufficiently, there
is no need to control both.
with a 2ps period with a 2 angstrom oscillation, for example, it seems
to me, that the energy asserted by the wall motion itself will
dominate, so requiring that the wall is thermostatted as well, would
not really make that much of a difference. you can simply quantify
this by setting up a simulation of a immobile, but thermostatted wall
with an equilibrated medium next to it, but then running the wall
adjacent medium with fix nve and observe the energy transferred and
compare that result to the same setup with a wall that is controlled
by fix move.

i am also wondering what kind of process this is modeling. after all,
a 500GHz vibration corresponds to lower infrared and the average
velocity of the wall approaches the speed of sound in dense media.

axel.

>
>> what frequency and amplitude of oscillation of the wall are we talking about here? axel. &gt; ------------------------------------------------------------------------------ &gt; Check out the vibrant tech community on one of the world's most &gt; engaging tech sites, Slashdot.org! http://sdm.link/slashdot &gt; _______________________________________________ &gt; lammps-users mailing list &gt; lammps-users@...6335.....sourceforge.net &gt; https://lists.sourceforge.net/lists/listinfo/lammps-users &gt;

--
Dr. Axel Kohlmeyer  akohlmey@...43...4...  http://goo.gl/1wk0
College of Science & Technology, Temple University, Philadelphia PA, USA
International Centre for Theoretical Physics, Trieste. Italy.

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