Hi, I have a question about the difference between the pressure values in case.md and case.castep (i.e., 1/3 * trace of stress tensor).

I had tried to run a simple MD simulatoin for melting some materials using CASTEP MD module (NVT ensemble with NHL thermostat). After the CASTEP MD simulation finished successfully, I can find the pressure values for all the MD steps in case.md file in working directory, though the unit of stored values are Hatree atomic unit. As you know these pressure values are identical with the pressure profile chart that can be obtained [CASTEP]-[Analysis]-[Energy evolution].

However, I had recognize the problem when comparing the pressure values from case.md file and that from the stress tensor in case.castep file. The calculated running average values of pressure (from case.md file) are significantly different from the result from stress tensor in case.castep file.

Now, my question is that, why the pressure values stored in case.md file are different from the value which is calculated from the stress tensor in case.castep file (1/3 * trace of stress tensor).

Do the pressure values from the case.md file include only the kinetic pressure term in general pressure tensor (i.e., not including the effect of interatomic forces)? The calculated values, i.e. (1) pressure values from case.md file and (2) pressure calculated from the stress tensor in case.castep file.

Regards, YOOSOO