Thermostat and manostat in fix command in Lammps

LAMMPS LAMMPS General Discussion
1

Hi there, regarding the npt ensemble in the fix command in Lammps, its Manual shows that, for example,

fix 2 all npt temp 300.0 300.0 100 xyz 1.01 1.01 1000
timestep 0.001

That is, the Tdamp is 100 and the Pdamp is 1000 time steps, respectively. And, it could also assume that a time unit of metal in current Lammps version is ps (picosecond), right ??

However, recently my one coleague told me that a time unit of metal in current Lammps version was fs (ficosecond), so above the command should be wr-written as follows

fix 2 all npt temp 300.0 300.0 0.10 xyz 1.01 1.01 1.00 drag 1.0
timestep 0.001

My question: which of abvoe handwriting command is correct ??!!

2

If you read the manual carefully you will see that Tdamp and Pdamp have time units. In the case of metal units they are ps.

If you want Tdamp to be 100 time steps the documentation gives you an easy way to do it, namely:
fix 1 all nvt temp 300.0 300.0 $(100.0*dt)
dt will by substituted by the current time step and so the Tdamp will be exactly 100 time steps.

So, to answer your question, the second command is correct, since you are doing 100*dt and 1000*dt manually.

3

Another question: how to use the darg term in the fix npt command ??

4

and, dt term should be determined by “variable” command in Lammps, right ??

5

fs stands for femtosecond. there is no such thing as a ficosecond.

Why depend on a colleague, when you can get authoritative info from the LAMMPS manual?

6

Please study the documentation about what the flag means and what it does. That is what it is for.

7

No.