How to calculate stress tensor in LIGGGGHTS .

Submitted by deepakpawar.2310 on Sat, 06/15/2019 - 19:45

Hello Friends

I am doing a small exercise to match the axial direction stress (sigma_zz) using the following two commands
(1) ave/time
(2) stress/atom

In order to calculate the axial stress from ave/time, perhaps I need to divide the z-direction force with piston area.
And from stress/atom command, I guess, will get directly the axial stress (sigma_zz) by using the following snippet

compute as all stress/atom ke pair
compute p all reduce sum c_as[1] c_as[2] c_as[3] c_as[4] c_as[5] c_as[6]
variable sigma33 equal -c_p[3]

I guess both the stress is suppose to match, However its not matching in my case.

Where I am doing wrong AND I THINK my approach seems to correct.

Any COMMENT/help will be highly appreciated! Thanks

Thao | Tue, 03/29/2022 - 00:18

Hi deepakpawar,

I also have the same confusion when these results do not match for me as well. Have you found the reasons or new ways to validate the calculation of axial stress?

Thanks so much.