The operating pressure of lammps fluctuates violently under the npt series.

LAMMPS LAMMPS Beginners
1

“#LAMMPS input file for Fe alloy aging at 500C and 10.3 MPa
#units and dimensions
units metal
dimension 3
boundary p p p
atom_style atomic
timestep 0.001 #1fs
neighbor 2.0 bin
neigh_modify every 2 delay 10 check yes

Atom definition

read_data Fe19Cr.data

Potential

pair_style eam/alloy
pair_coeff * * FeCr.eam.alloy Fe Cr

minimize

minimize 1.0e-4 1.0e-6 10000 100000

thermo 1000
thermo_style custom step temp pe ke etotal press vol

temp and press

fix 1 all npt temp 773.0 773.0 0.1 iso 103 103 1.0

out put

dump 1 all atom 1000 fe19cr-aged.xyz
run 200000” This is my in file.

微信图片_20230627101959
微信图片_202306271019591156×243 22.4 KB

2

Fluctuations in pressure and temperature are expected for finite systems, particularly for smaller ones. Condensed matter is not very compressible and thus pressure fluctuates much more than temperature. What matters in both cases is the average over particles and time.

There are many discussions on this subject in the archive. Please have a look around and (ultimately) into a statistical thermodynamics text book, if you want to learn more.

3

ok, I get it. Thank you.