[gmx-users] PRESS-XX, PRESS-YY, PRESS-ZZ in .edr file

[Anh Vo]

Dear Dr. Spoel,

I understand that pressure here is the stress tensor with 6 components
(PRESS-XX, PRESS-YY, PRESS-ZZ, PRESS-XY, PRESS-YZ, PRESS-XZ in 6
dimensions), but I'm not sure if it is the per-atom stress tensor (averaged
for all atoms), or the stress of the whole system?
And for the PRESSURE, does it represent the pressure on the whole
simulation system?

Thank you very much for sharing your time.

> Hi all,
>
> I have searched online and GROMACS documentation for this question but I
> haven't found any clear definition yet. Please help me to clarify it.
>
> In the output .edr file, there are PRESS-XX, PRESS-YY and PRESS-ZZ
options.
> What do they represent? Are they principal pressures (stresses) averaged
for
> all atoms during the simulation?
> What is the difference between those options and PRESSURE option?
>
> Thank you very much.
>
> Best,
> Anh Vo
>
THe pressure is a tensor, see manual.

-- 
David van der Spoel, Ph.D., Professor of Biology
Head of Department, Cell & Molecular Biology, Uppsala University.
Box 596, SE-75124 Uppsala, Sweden. Phone: +46184714205.