[lammps-users] about NPT

Dear all,

I just did a simplest npt relaxation as follows, but found that the temperature didn’t reach the required value, though pressure was controlled well. Why should that happened and how to improve on that? Thanks in advance.

units metal
boundary p p p

atom_style atomic
lattice fcc 3.61
region box block 0 4.0 0 4.0 0 4
create_box 1 box
create_atoms 1 region box

pair_style eam
pair_coeff * * Cu_u3.eam

neighbor 2.0 bin
neigh_modify delay 5

compute new3d all temp

velocity all set 0 0 0
fix 1 all npt 300 300 1 xyz 0 0 1 drag 2.2

thermo 10
thermo_modify temp new3d

dump 1 all atom 100 dump.init

timestep 0.001
run 10000

And follows are results:

Step Temp E_pair E_mol TotEng Press Volume
0 0 -906.21739 0 -906.21739 5803.5448 3010.9364
10 5.3807295e-26 -906.21876 0 -906.21876 5624.1233 3011.3196
20 2.8468179e-25 -906.22081 0 -906.22081 5343.4487 3011.9196


9980 3.9359031e-22 -906.24 0 -906.24 1.6762658e-07 3023.4645
9990 3.9463024e-22 -906.24 0 -906.24 1.6760086e-07 3023.4645
10000 3.9886493e-22 -906.24 0 -906.24 1.6762016e-07 3023.4645

2008-11-25

What does the temperature do when you just run NVE?
I'd try to figure what about your system is making T = 1.0e-22.
I don't think it is NPT by itself.

Steve