[lammps-users] [Puzzle] Fix box/relax command

Hi,

When using fix box/relax command, NULL means the box dimension remains unchanged. However, when I used the command like

fix 1 all box/relax aniso 0.0 0.0 NULL vmax 0.001
minimize 1.0e-6 0.001 1000 10000

on crystalline (metal), the box of z direction changes with the interaction step.

The output is just like

fix 1 all box/relax aniso 0.0 0.0 NULL vmax 0.001
minimize 1.0e-6 0.001 1000 10000
Memory usage per processor = 2.4531 Mbytes
Step PotEng Temp Pxx Pyy Pzz Lx Ly Lz
2 -3058.0128 0 12602.513 12602.513 17235.769 21.690007 21.690007 21.473127
3 -3058.1568 0 10433.127 10433.127 14745.085 21.696448 21.696448 21.4946
4 -3058.2767 0 8290.2932 8290.2932 12279.459 21.702801 21.702801 21.516073
5 -3058.3729 0 6178.6947 6178.6947 9842.7105 21.709028 21.709028 21.537547
6 -3058.4456 0 4107.3701 4107.3701 7442.3148 21.715059 21.715059 21.55902
7 -3058.4955 0 2096.4928 2096.4928 5095.2335 21.720742 21.720742 21.580493
8 -3058.5239 0 205.17797 205.17797 2851.1198 21.725631 21.725631 21.601966
9 -3058.5333 0 -754.38636 -754.38636 1601.1031 21.726559 21.726559 21.616596
10 -3058.538 0 1426.4421 1426.4421 3051.078 21.704869 21.704869 21.629586
11 -3058.538 0 1426.4421 1426.4421 3051.078 21.704869 21.704869 21.629586

Another problem is that the desired pressure is not accurate as the manual pointed. I wandered why and can anyone give me some suggestions?

Thanks!

What is your boundary condition in z?

Re: pressure values - do your atoms have velocities?
If so, read the doc page for fix box/relax.

Steve