VASP NPT Molecular Dynamics

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Hrishit Banerjee · #1 Post by **Hrishit Banerjee** » Fri Oct 04, 2013 4:06 pm

VASP has recently included NPT molecular dynamics in its recent release. However certain things are not clear till now, neither in the manual nor here in the forum.
Firstly, Whether SMASS value is required for an NPT molecular dynamics calculation along with PMASS and what should be the value?What values of PMASS should be chosen and what does the parameter value PMASS depend on?
Next, What values of LANGEVIN_GAMMA and LANGEVIN_GAMMA_L are required?does this affect temperature convergence?
The problem I am facing while increasing temperature along with NPT MD is that the temperatures in the OSZICAR file far overrides the TEEND specified in the INCAR.DOes someone have a solution to this problem?
Also it is to be mentioned that while thermalising the system is not reaching convergence point with the given values of EDIFF and EDIFFG.I have tried both large and small values of LANGEVIN_GAMMA and LANGEVIN_GAMMA_L.does anyone have a solution to this problem?

#2 Post by **admin** » Mon Oct 07, 2013 4:30 pm

In NPT dynamics SMASS is not defined. Because of large differences between different systems there are no default values set for LANGEVIN_GAMMA and LANGEVIN_GAMMA_L. You need to perform a couple of tests to find proper values. Read the manual:
http://cms.mpi.univie.ac.at/vasp/vasp/P ... ostat.html
http://cms.mpi.univie.ac.at/vasp/vasp/P ... amics.html

Hrishit Banerjee · #3 Post by **Hrishit Banerjee** » Wed Oct 16, 2013 7:08 am

Could you please comment on how the problem of convergence can be solved for NPT dynamics which formed the last part of my question.

mghosh · #4 Post by **mghosh** » Wed Sep 09, 2020 5:54 pm

Any update on this question? Still looking for an answer.

#5 Post by **ferenc_karsai** » Mon Sep 14, 2020 8:26 am

Concerning your first question, your true temperature will always oscillate around your temperature defined in the INCAR. If it is far away from that value then you need to equilibrate or have simply a wrong structure.

If you see that your electronic calculations are not converging, then you need to tweak your parameters for the electronic calculation.
That should normally be an independent problem from the motion of the atoms, except something goes wrong there and you get phyisically incorrect configurations.

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