Particles velocities are not corresponding to the temperature

Hello Everyone I am studying defect dynamics in sic, for now I am doing NVT followed by NPT to get equilibrium, I have seen equilibrium and i have seen constant temperature and energy (offcourse very small oscillation), The only problem is very small MSD or you say particle velocities are not corresponding to the high temprature in the dump,

I have attached the damp file and plotted thermodynamic variables. can anyone comment on. this ?
please accept my best regards
Irslan Ullah Ashraf
dump.cvac.2000 (5.6 MB)

Hi @Irslan_Ullah_Ashraf,

There is very little anyone can possibly say about your problem with the very little information you provide here.

  • MSD and instantaneous velocities are two different things. Are your particles only supposed to diffuse in your system? Did you look at your simulation in a visualisation software like Ovito or VMD?
  • Since the temperature is directly computed from the kinetic energy of your particles, if you think that velocities and temperature do not match, we will need a more detailed analysis. There is no reason to think that this is the case if you do standard MD.
  • The dump file contains no information with regard to the particles velocities, only non-consecutive positions. We can’t say anything about it.
  • This is a constant volume simulation dump, it cannot correspond with the plots you show.

Youŕe also not specifying important details like the LAMMPS version and the model you’re using, which makes it totally impossible to give meaningful inputs on your results.


This statement makes no sense at all, since the temperature is computed from the particle velocities. Please keep in mind that velocity does not automatically correspond to mobility, if mobility requires activation, that is a barrier must be crossed.

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