# is it normal to have energy drift upward in nve ensemble?

Hello LAMMPS community,

I ran an equilibrium simulation cell with NVE and Langevin thermostat. There is a cutoff radius of 3*sigma. I observe the potential and total energy drift, as attached below (for potential energy). Kinetic energy, as expected, doesn’t experience any drift.

This issue has been discussed a few times in the mailing list, some of them are here and here. I understand that introducing the cutoff radius may gradually shift the energy. Is it completely normal?

Anh Tran

Hello LAMMPS community,

I ran an equilibrium simulation cell with NVE and Langevin thermostat. There

1) with fix langevin in addition to fix nve, you do *not* have an NVE ensemble.

is a cutoff radius of 3*sigma. I observe the potential and total energy
drift, as attached below (for potential energy). Kinetic energy, as
expected, doesn't experience any drift.

This issue has been discussed a few times in the mailing list, some of them
are here and here. I understand that introducing the cutoff radius may
gradually shift the energy. Is it completely normal?

2) this has nothing to do with the energy offset at the cut off (at 3
sigma, it is not really large anyway).
up on equilibration.

please keep in mind that this mailing list is not a classroom for
learning MD. both issues i commented on are something that you should
(have) discuss(ed) with whoever is your teacher in MD.

axel.

Hello LAMMPS community,

I ran an equilibrium simulation cell with NVE and Langevin thermostat. There

1) with fix langevin in addition to fix nve, you do *not* have an NVE ensemble.

is a cutoff radius of 3*sigma. I observe the potential and total energy
drift, as attached below (for potential energy). Kinetic energy, as
expected, doesn't experience any drift.

This issue has been discussed a few times in the mailing list, some of them
are here and here. I understand that introducing the cutoff radius may
gradually shift the energy. Is it completely normal?

2) this has nothing to do with the energy offset at the cut off (at 3
sigma, it is not really large anyway).