hi,there!

i have been working to compute the pressure of a group of water molecules in a box but not all the molecules.

i tried compute stress/atom and compute reduce sum but the the pressure got fluctuated intensely .

then i tried compute chunk/atom and want to but now i have no idea about my original plan .

can u provide some method to do that?

thanks inadvance!

hi,there!

i have been working to compute the pressure of a group of water molecules

in a box but not all the molecules.

i tried compute stress/atom and compute reduce sum but the the pressure got

fluctuated intensely .

microscopic pressures *do* fluctuate massively. the more the smaller

the group/volume is.

pressure, like temperature, is a bulk property and we can only compute

it microscopically because we assume equipartitioning, i.e. a system

in equilibrium and then you can average over time as well as over

volume.

this whole "how to compute pressure of subsets of a system" has been

discussed on this mailing list so many times, that most people handing

around here since a long time ago and growing tired of it. please

study those many discussions in the mailing list archives, and

correlate this with what you find in a text book on statistical

thermodynamics and then be enlightened.

axel.