About "compute pressure command "

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1

Dear Everyone,

I just have a simple question on the “compute pressure command .” The doc page is http://lammps.sandia.gov/doc/compute_pressure.html

If I use the keyword, for example: virial or ke
then will the values output from Lammps are instantaneous or averaged values?

Thank you for your time and help.

Lili

2

Dear Everyone,

I just have a simple question on the "compute pressure command ." The doc
page is http://lammps.sandia.gov/doc/compute_pressure.html

If I use the keyword, for example: virial or ke
then will the values output from Lammps are instantaneous or averaged
values?

instantaneous, of course. for averaging there is fix ave/time.

axel.

3

Thanks Axel. BTW, the pressure tensor equation in the doc page looks different than the definition of the Virial stress in

http://en.wikipedia.org/wiki/Virial_stress

Does Lammps use some other definition for Virial stress? Just want to make sure.

Many thanks,
Lili

4

Thanks Axel. BTW, the pressure tensor equation in the doc page looks
different than the definition of the Virial stress in

http://en.wikipedia.org/wiki/Virial_stress

Does Lammps use some other definition for Virial stress? Just want to make
sure.

not really, if you look at it closely. the first term can be
simplified because you have no center of mass velocity (usually) and
the second terms are equivalent for all simple pairwise additive
potentials with no bonds or other interactions.

axel.