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Re: [ESPResSo-users] NPT Isotropic with P3M activated

From: Olaf Lenz
Subject: Re: [ESPResSo-users] NPT Isotropic with P3M activated
Date: Fri, 25 Feb 2011 10:56:05 +0100
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On 02/24/2011 10:51 PM, Salvador H-V wrote:
> Then, if I understood well, the new release of ESPResSo will have 
> code for non-cubic P3M, so, I should be worry only about the MC 
> movements.

Exactly! Be aware that the non-cubic P3M code is very recent. We believe
that it works fine and we have done tests, but if you get strange
results, this might be the place too look. Also, we are very happy if we
have somebody else testing the code!

> At this point I would like to drop a question: In order to implement
>  the MC algorithm in Tcl, I just need to save the energies (old and 
> new) and the configuration of the particles and then use the MC 
> scheme to attempt a change in the x & y directions?

Yes, that should be it. I am not aware of a script that has done this so
far, but it should be very simple to write.

Note that when you do a volume move, you have to think of a few things
to make sure detailed balance is kept and that you have to use an
effective Hamiltonian that takes into account the density of states.
Have a look at Frenkel/Smit "Understanding Molecular Simulation", or
have a look at appendix A of my thesis

Instead of saving the last configuration, it should also be OK to resize
the box back in case of rejection. Note that there is even the function
"change_volume" that allows you to resize the box using a single function.

If you have a running script, we would be very interested to get some
code from you. It might be very useful to extend ESPResSo by a function
to do constant pressure MC moves!

Dr. rer. nat. Olaf Lenz
Institut für Computerphysik, Pfaffenwaldring 27, D-70569 Stuttgart
Phone: +49-711-685-63607

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