Calculate pressure under NVT condition

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1

Dear All,
Here is my typical geometry of the system, which I simulate a sphere of atoms in a large box:

units metal
atom_style atomic
lattice fcc 4.0687
region box block -150 150 -150 150 -150 150 units box
region particle sphere 0.0 0.0 0.0 60 units box
create_box 1 box
create_atoms 1 region particle

When I output the pressure information after running NVT ensemble (at several different temperatures), the mean value of the pressure is around zero, and the fluctuation is less than 5 bars. However, according to the Laplace pressure equation: P_diff=2*gamma/R, where assuming gamma=0.6J/m^2 (surface energy), R=6nm, thus P_diff=2000 bars. Thus can I get zero pressure not 2000 bars from the prediction?
As I understand, the pressure refers to the overall system of atoms.

Best regards,
Leo

2

An isolated system, i.e. a small particle in a big box, does not have “pressure”. Surface tension is the more appropriate term, which is not equal to the value output by the “press” keyword. You need to look at stress/atom and figure out the difference in stresses due to surface tension.

Ray