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?
Thank you for your inputs.
Anh Tran
two comments on this:
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).
instead, please pick up your text book on molecular dynamics and read
up on equilibration.
Thank you for your inputs.
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.
two comments on this:
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).
instead, please pick up your text book on molecular dynamics and read
up on equilibration.
oh, and here is a bonus advice: you probably should also read up on
energy conservation and by what it is affected, as this is something
that has to be considered in this context as well.
axel.
Axel,
Many thanks for your comments. I appreciate it.
-Anh