[lammps-users] Diffusion estimation

Dear Alex,
Thanks for your quick response. I understand the issue. According to your message, I am writing in a new thread.

As I understood from your discussion, out of the following steps for preparing glass for estimating diffusion at 3000K, I need the-

  1. velocity mixing (nvt) at 4000K for 10 ps
  2. Relaxation at 4000K (npt) 30 ns
  3. Cooling from 4000K to 3000K at zero pressure (npt) 1K/ps
  4. Relaxing at 3000 K at zero pressure (npt)
  5. Statistical averaging over 1000 ps (nvt) at 3000 K.

As per your suggestions, I need to put msd immediately after step no 4 i.e. fix NPT. However, is it ok to have fix nve or fix npt at the final step no. 5 of statistical averaging (for different temperatures, say at 3500K, 3000K …1500K) for msd evaluation??

This is for estimation of Ea i.e activation energy in Arheneous regime. As I think the diffusion needs free motion at a particular temperature, so temperature & pressure should be precisely defined. Therefore volume and energy shouldn’t be constrained i.e. should be allowed to vary. So to me fix NPT is a good ensamble for this property evaluation.

I still have doubt in using either fix nve, fix nvt, or fix npt, at step no. 5. Which one will yield proper results??
What are your views??

Thanks and regards
Mukesh Pandey

I cannot comment any further on the science as this is not my area of research. It would be off-topic for this mailing list anyway.