[lammps-users] which parameters should I tune for my npt ensemble?

Hi,
I want to simulate the melten at 1800K and 1 atmostphere.
i uses the commands
“units real
fix 1 all npt 1800.0 1800.0 10.0 xyz 1.0 1.0 400.0 drag 1”

the screen output is

Step Temp E_pair E_mol TotEng Press Volume
0 1800 5187508.9 0 5214158.9 7216181.4 49046.786
1000 1832.9795 -3781557.9 0 -3754419.6 -6076.0394 119674.93
2000 1837.293 -3810607. 0 -3783405.3 4634.3511 114077.72
3000 1807.2595 -3905987.5 0 -3879230 -3869.2594 110968.86
4000 1784.468 -3905447.6 0 -3879027.6 3928.4849 108175.89
5000 1753.3083 -3957619.6 0 -3931660.9 -3709.7621 106404.35
6000 1847.0305 -3970968.1 0 -3943621.8 -1723.3971 105110.21
7000 1770.9675 -3969437.4 0 -3943217.2 -3606.5073 104249.
8000 1820.9645 -3981412.1 0 -3954451.7 -4053.1403 103133.9
9000 1808.4899 -3963224.2 0 -3936448.4 3268.6735 102394.53
10000 1801.359 -4037523.7 0 -4010853.5 -12200.337 101492.1
As expected, the temperature is reduced to 1800K or so,I want to know what is the unit of the press column? Why don’t they reduce to 1 atmosphere as i expected? And what’s the negative pressure mean?
Which parameters should I tune for my fix purpose?
Thank you for your instruction.

在2007-06-08,[email protected]…42…e.net 写道:

Units of pressure are discussed in the docs on the units command
page. For only 150 atoms, large fluctuations in pressure (including
negative) are normal for MD.

Steve