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Re: [lammps-users] NPT equilibration - very high pressure

Re: [lammps-users] NPT equilibration - very high pressure

 From: Kristof Bal Date: Mon, 24 Jul 2017 18:23:53 +0200

On Jul 23, 2017 14:37, "Meral Sharkas via lammps-users" <lammps-users@...76...ts.sourceforge.net> wrote:
Dear Team,

I hope if you can help me with my problem and in all ways thank you for your enormous help in this mailing list.

After energy minimization, I was trying to equilibrate my system with NPT ensemble at 300 K at P=0 with "metal" units. I used the following commands but the pressure during simulation is extremely high and was equilibrated P=3800 bar. Can you pleased advise if i am applying the equilibration technique in a wrong way or not?

min_style cg
minimize 1e-25 1e-25 5000 100000

Step Atoms Temp Press PotEng KinEng TotEng Volume Density
8     1566          300    3430.0525   -4304.4565    60.687638   -4243.7688    14097.888    4.6156103
100     1566          300    3430.0525   -4304.4565    60.687638   -4243.7688    14097.888    4.6156103
200     1566          300    3430.0525   -4304.4565    60.687638   -4243.7688    14097.888    4.6156103
......
1000     1566          300    3430.0525   -4304.4565    60.687638   -4243.7688    14097.888    4.6156103
1008     1566          300    3430.0525   -4304.4565    60.687638   -4243.7688    14097.888    4.6156103

fix                     1 all npt temp 300.0 300.0 100 aniso 0.0 0.0 1000

The time constant of pressure equilibration is 1 NS in your input, meaning that you'd only see appreciable pressure changes after very long runs. So what about trying more appropriate values for these damping constants?

Kristof

1008     1566          300    3430.0525   -4304.4565    60.687638   -4243.7688    14097.888    4.6156103
1100     1566      265.962    3962.7618    2210.6141    53.802018    2264.4161    14097.888    4.6156102
1200     1566    256.76105    4928.4334    4541.8625     51.94074    4593.8033    14097.889      4.61561
1300     1566    267.04746    5274.6659    3633.5111    54.021599    3687.5327     14097.89    4.6156097
1400     1566     279.8136    5215.5371    1841.4099    56.604088     1898.014    14097.891    4.6156093
......