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[ESPResSo] Specification of External Potential/Force

From: Lorenzo Isella
Subject: [ESPResSo] Specification of External Potential/Force
Date: Tue, 19 Feb 2008 15:11:10 +0100
User-agent: Mozilla-Thunderbird (X11/20080110)

Dear All,
I think I have a quite unusual problem here.
I am often (ab)using Espresso to investigate systems and problems quite far away from molecular dynamics. Now, I would like to consider a system in 3D where you have a pair-wise interaction between particles (not relevant right now, but you can think of a Lennard-Jones potential) plus an external potential acting on the system. To fix the ideas, think of a strong harmonic confinement along z, i.e. V_z=K_z*z^2 and of a much milder confining potential in the xy plane i.e. V_{xy}=K_{xy}(x^2+y^2), with K_z>>K_{xy}. This is intended to give rise to rather flat structures along along z (together with an interaction potential having a hard-core repulsion). (1) Is this doable in Espresso? Can one tune the external force/interaction in a similar way as one can do with the tabulated interaction potential?
In the documentation I bumped into:

[ext_force x value y value z value] An additional external force is applied to
the particle.

when discussing particle properties, but I am not sure this allows me to do exactly what I have in mind [See page 26 of the user guide]. (2) If I turn off the thermostat, am I using Espresso for deterministic molecular dynamics? Am I then removing the "noise" (apart from numerical round-off errors) from the simulation?

Many thanks


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