Extranting thermal forces

I am calculating the energy of my sample for different temperatures and I would like to know, for a given atom, the interatomic forces for each temperature. Do the interatomic forces change with different temperatures? How can I extract that information from LAMMPS?

Thanks.

I am calculating the energy of my sample for different temperatures and I

what "energy"? there are all kinds of energies.

would like to know, for a given atom, the interatomic forces for each
temperature. Do the interatomic forces change with different temperatures?

for normal simulations forces only depend on the relative positions of
the atoms. please see the corresponding potential functions.

How can I extract that information from LAMMPS?

forces on each atom can be output in custom style dumps as fx, fy and
fz properties.

axel.

Almost all pair styles in LAMMPS depend only

on the coords of atoms, not their velocities (where

velocities are affected by temperature). Exceptions

are granular pair styles and DPD.

Of course if you run a system at a higher temp,

the atoms will move differently, which will lead

to different coords and forces.

Steve

Hello,

I know that for a given interatomic potential, the interatomic forces only
depend on the positions. Also I know that for a certain temperature, doing
NVE, by using a thermostat you can introduce in the system a dynamical
variable that represents the friction in the sistem until the temperature is
equal to the desired value, where this dynamical variable is related to the velocity of the praticle.

I want to know if you can extract that, the complete term in the right side
of the Newton equation (interatomic force + friction term), so I get a force
depending on the temperature.

All the thermostat fixes (e.g. nvt, langevin) have extra quantities

to the system). See their doc pages.

Steve

Hello,

I know that for a given interatomic potential, the interatomic forces only
depend on the positions. Also I know that for a certain temperature, doing
NVE, by using a thermostat you can introduce in the system a dynamical
variable that represents the friction in the sistem until the temperature is
equal to the desired value, where this dynamical variable is related to the
velocity of the praticle.

so you are talking about a langevin thermostat here, right?
not all thermostat algorithms work this way and for a system in
equilibrium, those terms should usually be small and cancel out on
average.

I want to know if you can extract that, the complete term in the right side
of the Newton equation (interatomic force + friction term), so I get a force
depending on the temperature.

for langevin, you have *two* additional terms to consider, a friction
term and a random term.
both of them are included in the forces output in custom dumps (as are
any other force manipulations due to fixes).

axel.