|From:||Steve Plimpton <sjplimp@...24...>|
|Date:||Thu, 15 Jun 2017 08:06:26 -0600|
Hi,I have been running some MD simulations using fix efield, and noticed that "something strange" was going on with the pressures that I was getting out... so I did some tests.Consider a single, rigid, diatomic molecule, aligned with the z-axis, in a non-periodic simulation cell, at zero temperature. (I.e. all of the atoms are at rest.)The molecule carries no net charge, but the individual atoms have charges of +1e and -1e respectively. There are no forces defined between the atoms, and the geometry of the molecule is kept constant using fix shake.What do I do?I run the simulation, from this starting point, using the NVE time integrator, and monitor the pressure.What do I expect?That the pressure should be zero, because the atoms are at rest, and there are no forces between them. Even under an applied (constant, uniform) field, a rigid dipole could experience a torque, but no net force.What do I observe?That the pressure returned by the "thermo" keyword scales linearly with the applied field.Why might this be?
- [lammps-users] Pressure with an applied E-field
- From: Matthias Kahk <matthiaskahk@...24...>