[gmx-users] Energy conservation in collision
gmx3 at hotmail.com
Fri Apr 27 12:23:44 CEST 2007
>From: Janne Hirvi <janne.hirvi at joensuu.fi>
>Reply-To: Discussion list for GROMACS users <gmx-users at gromacs.org>
>To: gmx-users at gromacs.org
>Subject: [gmx-users] Energy conservation in collision
>Date: Thu, 26 Apr 2007 17:36:29 +0300
>I am still struggling with the energy conservation in the system where a
>droplet (consisting of rigid molecules) collides with a frozen structured
>surface. The total energy is well conserved at the beginning of NVE
>when the droplet is approaching the surface and once again when the droplet
>stabilized on the surface, but the drift or fluctuation in the total energy
>observed between these extremes.
>The total energy of the system (~300 000kJ/mol) decreases slightly
>at the collision and on non-wetting surfaces (water droplet wont intrude to
>pores of the surface) part of the energy reverts quickly causing a sharp
>in the energy curve. This could indicate an integration error at the
>due to the large time step, but equal behavior is observed with the time
>of 2.0fs and 0.5fs.
>On the wetting surfaces (water droplet intrude to the pores of the surface)
>center of mass motion of the droplet come to a stop at the collision as in
>case of non-wetting surface and sharp decrease in the total energy is
>However, now none of this energy is reverted and the total energy stabilize
>this value until the water molecules starts to intrude to the pores of the
>surface. The total energy decrease slowly in conjuction with the slow
>of the height of the center of mass of the water droplet until the bottom
>the pores is reached. After the bottom of the pores is reached energy will
>stabilize to the corresponding value which is about 200-300kJ/mol lower
>Decreasing the time step from 2.0fs to 0.5fs have no influence for the
>conservation and somehow the problem seems to be connected to water-surface
>interactions: on the wetting surfaces (more water-surface interactions) a
>is observed instead of a sharp peak of non-wetting surfaces (less
>interactions). Any ideas how I could achieve complete energy conservation?
>Thanks for your time and help,
What kind of interactions are you using?
Plain cut-off for Coulomb and LJ will give bad energy conservation.
For your system you probably want to use shifted LJ and Coulomb potentials.
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