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-
- velocity mixing (nvt) at 4000K for 10 ps
- Relaxation at 4000K (npt) 30 ns
- Cooling from 4000K to 3000K at zero pressure (npt) 1K/ps
- Relaxing at 3000 K at zero pressure (npt)
- 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