Dear Ray Shan,
I just want to know is the virial calculation of stress, the true stress or
engineering stress? i meant following command in LAMMPS compute true stress
* Volume or engineering stress * Volume?
compute 1 all stress/atom
fix 1 all ave/atom 1 100 100 c_1
compute 2 all reduce sum f_1
Neither. True or engineering stresses are only meaningful in a
tensile test. Compute stress/atom is a general formulation and does
not know if you are calculating true or engineering stresses. To do
so, just go back to the definition of these stresses, i.e., obtain the
load and the area and estimate the true or engineering stress based on
the area you chose.
I am not sure what your commands will give you. Sum of an averaged
value that is averaged over 100 steps? Not sure what that is.