granular system integration

Hello!

I am simulating hybrid granular system with complex particles, using fix rigid/small. Could you please make a reference to some explanation how the frictional forces are computed in nve integration. I want to understand how the energy dissipation due to these forces is computed. As I understand nve means conservation of energy.

Oksana

Hello!

I am simulating hybrid granular system with complex particles, using fix
rigid/small. Could you please make a reference to some explanation how the
frictional forces are computed in nve integration. I want to understand how
the energy dissipation due to these forces is computed. As I understand nve
means conservation of energy.

your question is too vague. please be more specific and best provide a
simple example because it is not even clear from your description what
your atom style and general setup is.

nve does not mean "conservation of energy". nve means no (kinetic)
energy added or removed by the integrator.

axel.

Thank you for the fast reply!

Well, yes the question is rather vague, because it concernes understanding of principles. I have performed calculations with nve integrator (according to LAMMPS how-to for granular systems) and I want to understand how it is working not diging into C++ code. There should be some described algorithm in litterature, I think, I just do not know where they are.
My system is hybrid sphere dipole bond, pair_style hybrid/overlay gran/hertz/history and dipole/cut. Spheres with dipole moments are grouped in rigid bodies by fix rigid/small molecule, LJ is turned off by coefficient. I study micro granular particles with moments and friction in the external field, so that is mecanical-dipole system.
So if there is a dissipative force (like friction) the energy will be dissipated in the system using nve? And forces are calculated explicitely from the equations described for pair styles, e.g. in the manual, with no regard to energy?

Oksana

Четверг, 30 января 2014, 7:46 -05:00 от Axel Kohlmeyer <akohlmey@…24…>:

Thank you for the fast reply!

Well, yes the question is rather vague, because it concernes understanding
of principles. I have performed calculations with nve integrator (according
to LAMMPS how-to for granular systems) and I want to understand how it is
working not diging into C++ code. There should be some described algorithm
in litterature, I think, I just do not know where they are.

LAMMPS uses Velocity Verlet for time integration. fix nve implements
the pure form of it with no additional manipulations. practically
every text book on MD describes it. having a look at the sources would
have shown you.

My system is hybrid sphere dipole bond, pair_style hybrid/overlay
gran/hertz/history and dipole/cut. Spheres with dipole moments are grouped
in rigid bodies by fix rigid/small molecule, LJ is turned off by
coefficient. I study micro granular particles with moments and friction in
the external field, so that is mecanical-dipole system.
So if there is a dissipative force (like friction) the energy will be
dissipated in the system using nve?

this makes no sense. it has been explained many, many times that fix
nve does *not* manipulate energies. *that* is what makes the NVE
ensemble (if everything else is consistent with it).

And forces are calculated explicitely
from the equations described for pair styles, e.g. in the manual, with no
regard to energy?

unless it is explicitly specified, the integrator does not regard
anything but the force on the position of the particle (which is
usually a point particle).

axel.

Thank you very much, you closed all my doubts and questions.
Oksana

Четверг, 30 января 2014, 9:04 -05:00 от Axel Kohlmeyer <akohlmey@…24…>: