Hi, I have a quuestion about the difference between the calculated pressure values from Forcite analysis and CASTEP stress tensor.

I had tried to run a simple MD simulatoin for melting some materials using CASTEP MD module (NVT ensemble with NHL thermostat). As you know, after running the CASTEP MD simulation, windows for updating the energetic and structural evolution of input atomic structure are appeared, i.e., CASTEP Dynamics History windows: (1) Simulation Time (ps) vs. Pressure (GPa), (2) Simulation Time (ps) vs. Temperature (K), and (3) Simulation Time (ps) vs. Constant of Motion (eV), etc. And, this chart also can be obtained [CASTEP]-[Analysis]-[Energy evolution].

After the CASTEP MD simulation (finished successfully), I had tried to see the running average values of pressure profile during the CASTEP MD simuation using the analysis tool of Forcite module (as you know, there is no dynamical and statistical analysis tool in CASTEP analysis tool in MS 6.1). Then the calculated running average values of pressure profile from Forcite analysis show a good agreement with the chart of energy evolution analysis in CASTEP anaysis tool.

However, I had recognized the problem after comparing the calculated pressure values from Forcite analysis and pressure estimated from the Stress tensor calculated from CASTEP. The calculated pressure values from Forcite analysis (i.e. show a good agreement with Energy evolution analysis of CASTEP) show significantly different values from the pressure estimated from the stress tensor in CASTEP ([CASTEP]-[Properties]-[Stress]).

I tried to figure out the reason of this difference between calculated pressure values from Forcite analysis (or [CASTEP]-[Analysis]-[Energy evolution]) and CASTEP stress tensor, but I cannot understand it. Is there a significant difference between them in theoretical level?

Regards, YOOSOO