Hi everyone,

I would like to calculate the pressure tensor in a fixed group of atoms in the none-periodic boundary conditions. The calculation process is described as follows. I have used the compute stress/atom command to obtain the stress tensor for each atoms in the given group. I first wrote a code to sum up all the stress per atoms to obtain the total value. Then I have calculated the total length along x, y, z direction in this group according to the coordinate of atoms. In this way I can get the volume of this group. According to the relationship between the average pressure tensor and the sum of the stress tensor per atoms (Pij=sum(Sij)/volume), where Pij, Sij , volume are pressure tensor of in the fixed group, stress tensor per atom and group volume. Thus, I can obtain the pressure tensor for the given group.

For the above words, I have three problems. First, I want to verify whether the calculation process is correct. Second, if it is correct, I think the calculation for volume is quite rough, especially for the simulation with none-periodic boundary condition, since the the shape of the sample will become quite irregular during the deformation. Thus, we can not simply using the box volume with a orthogonal shape to replace the real deformed shape. Third, can LAMMPS output the pressure tensor directly just like the pxx, pyy, pzz… in thermo_style command?

Thank you very for your help.

Best Regards,

Suzhi Li