STRESS in NPT Simulation

[burakgurlek]

Hi,

I am running an NPT simulation and I wonder if one does not specify PSTRESS, Does VASP give a default value? At which pressure, pressure will be equilibrated?
I tried this and the simulation runs without error, but not sure what is happening.

Regards,
Burak

[manuel_engel1]

Hi Burak,

The default value for PSRESS if it is not specified is 0. I have added this information here on the VASP wiki. You can also obtain the actual value of PSTRESS used in your simulation by inspecting the vasprun.xml file: you may simply search for "PSTRESS" in the file or you may use this Xpath query:

Code: Select all

modeling/parameters/separator[@name="ionic"]/i[@name="PSTRESS"]

I hope that helps answer your question.

[burakgurlek]

Hi Manuel Engel,

Thanks for your info. So if PSTRESS=0, should I assume that the system is in the ambient pressure?

Regards,
Burak

[manuel_engel1]

In your case, i.e., for NPT molecular dynamics simulations, PSTRESS controls the target pressure of the barostat. If it is zero, that means there is no external pressure applied.

[burakgurlek]

Dear Manuel,

Thanks, if I set PSTRESS=0, is it ambient pressure? or I need to specifically set it to 1atm?

Regards,
Burak

[manuel_engel1]

You will need to specify it by setting PSTRESS equal to 1atm. However, keep in mind that PSTRESS is in kB, so you have to convert the value of 1atm to the correct units in kB first.