Temperature is halved when running the simulation.

User Group,

Please find attached my log file.

1: I set a temperature of 1300K. I have a total of 385 atoms, 192 fixed and 193 moving. I set the NVT fix only for the moving atoms. As seen from the log file, the temperature is approx halved when the simulation starts. Since the fix is not applied to the fixed atoms which have 0 KE and hence 0 temperature, shouldn’t all of it be concentrated only on the moving atoms?

2: When the temperature damping is reduced, the temperature is supposed to return to its original value of around 690K but it does not. Could anybody please tell me what could be the issue.


log .lammps (673 KB)

You didn't post your input script, but I assume the temperature
you are printing is the T for the whole system (which is the default).
So if half your atoms have 0 velocity, then T will be half what you
expect. Read the fix nvt or thermo_style and compute temp doc pages for info on
how to print out more specific temperatures.


For units metal, time is in pico-sec.

Your temp damping factor (from your log.lammps you used - fix 1 mobile
nvt temp 1300.0 1300.0 125.0) is 125 picosecs which is too large. Try
using 0.4 or something of that order for Tdamp.

This is a common error that gives half the temperature. I think the
reason for this is that half the energy supplied at the beginning of
the run (you used velocity mobile create 1300.0 4928459 dist gaussian)
gets equi-partioned.