Hi,
I have a 2D lattice under linear loading. The system follows the
Hamiltonian equations of motion, i.e., the work applied to the system will
be transferred to the total increase of internal energy.
I am not sure which ensemble i should use in this case. I don't have
thermostat or constant internal energy. The only constant is (total
internal energy - external work).
Can you give any suggestion on this?
Thank you,
Likun
Hi Likun,
It is not quite clear what kind of ensemble you are wish for. If,
quote, "the work applied to the system will be transferred to the
total increase of internal energy", and, quote "the only constant is
(total internal energy - external work)". Then does not this mean the
original internal energy of the system is conserved? Hence an NVE
ensemble?
Ray
Hi,
I have a 2D lattice under linear loading. The system follows the
Hamiltonian equations of motion, i.e., the work applied to the system will
be transferred to the total increase of internal energy.I am not sure which ensemble i should use in this case. I don't have
thermostat or constant internal energy. The only constant is (total
internal energy - external work).
please note "fix nve" doesn't mean, that the integrator
enforces constant (total) energy. all it means is that
it doesn't *change* the total energy, i.e. neither adds
or removes, which is likely what you are looking for.
axel.
Hi Ray and Axel,
Thanks for your reply. Sorry i still have some confusions.
The microcanonical ensemble NVE means that E is fixed, so the total energy
(potential + kinetic) should be constant throughout the dynamical process.
However, in my system, there is an increase of E which is equal to the
external work (from first law of thermodynamics). Obviously it is not
microcanonical ensemble.
When using 'fix nve', does it imply microcanonical ensemble?
best,
Likun
Likun,
Using an NVE ensemble does not mean that energy conservation is
enforced by the integrator. There is no guarantee that the total
energy should necessarily conserve when using fix nve. On the
contrary, when a system has an increasing total energy, it does not
necessarily imply that using fix nve is wrong. It was described that
"The only constant is (total internal energy - external work)", and
this constant sounds to me equals to the initial internal energy. The
system is being done work by the environment, together the system and
the environment (i.e. the universe) conserves energy.
If you apply linear loading to your system via fix move, displace_box,
velocity commands, or etc., I think applying fix nve to your system is
appropriate.
Cheers,
Ray