[lammps-users] question about the stress tensor of atom

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1

Maybe Aidan wants to comment. I think he will agree with what
I said originally.

Steve

2

Per atom stresses fluctuate strongly in time and space. The different
definitions will distribute those fluctuations differently. Once you average
over a moderately large chunk of space and/or time, these differences wash
out strongly.

We make a brief reference to the LAMMPs per-atom virial in our paper on the
virial calculation, which will give you some cover.

A. P. Thompson, S. J. Plimpton, and W. Mattson, "General Formulation of
Pressure and Stress Tensor for Arbitrary Many-body Interaction Potentials
under Periodic Boundary Conditions," J. Chem. Phys., 131 154107 (2009).

Aidan

3

Hi Aidan,

Thanks for your reply. Yes, I also searched the paper and now I’m reading it.

Another question, in the stress/atom command doc file, it’s said that the long-range Coulombic interactions contribution cannot be captured by the given atom stress equation. If so, how can I correctly calculated the atom stress for water like TIP3P, SPC models which need use the ewald sum or pppm method?

Thanks!

Dongshan

4

This has been discussed on the list many times. It's not
that LAMMPS simply doesn't do it. It's that we don't know
how to do it for PPPM. If you think about it, asking
what the long-range (infinite) contribution is to per-atom
stress or energy is not a well-formed question. There is no
obvious meaning to breaking a K-space contribution into
per-atom pieces.

Steve