[lammps-users] NVT reax

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1

Hi,all,

I am running a MD simulation using NVT ensemble. I use reax force field. Timpstep is 1fs, the simulation has ran for 10000 steps. I keep the temperature at 65 K,but it fluctuates to 400K, and not stable. Below is my input script
units real
dimension 3
boundary p p p
neigh_modify delay 0 every 1 check yes
atom_style charge

read_data data.psi

pair_style reax
pair_coeff * * ffield.reax 2 6

fix 1 all nvt temp 65.0 65.0 10.0 drag 0.2

thermo 10
thermo_style multi
timestep 1.0
restart 200000 restart.psi
run 1000000

dump 1 all custom 2500 dump.psi id type q x y z
run 100000

Before this simulation, I have ran another simulation of the same system.The only difference is that I set "drag 0.0’ in the fix command. I ran it for 1ns, the temperature is not stable,it even fluctuated to about 10000 K. Can anyone explain this and solve this problem?

Thank you!

2

Did you minimize the system before starting NVT?

3

Hi,

Yes, I used minimized structure.

4

1.0 fmsec may be too large a timestep for a ReaxFF model. I wouldn;t
use drag. I would instead inititialize the system to 65K. If you can
run NVE in a stable manner, then you should be able to use NVT.

Steve

5

Hi, Steve, Vikas, Gilbert,

Thank you for all your replies. I set the timestep to 0.5 fs, and till now the temperature seems to be stable around 65 K.

Chenchen