# How to control the cooling rate in lammps

Dear All,

I use

fix 2 all nve

fix 3 all temp/berendsen 4000 0 100

run 2000000

to simulate a cooling process with lammps. A I know, the cooling rate depends how long the time I run the simulation.

Thus, if the temperature decreases from 4000k to 0K in 400ps, the fooling rate will be 40K/ps, while running in 2000ps, the cooling rate would be 2k/ps, right?

But, from the output file, I found that after 400ps, the temperature just decreased to 2000K, not 0K. It means the cooling process did not finish.

So, how to adjust the parameters to sun an overall cooling process, especially in a short time?

Thanks

Regards

Yanan Lv

Institute for Frontier Materials

• Deakin University

Geelong Warunponds Campus

Victoria 3217 Australia
: E-mail: lyana@…3412…

Website: http://www.deakin.edu.au
Deakin University CRICOS Provider Code 00113B (Vic)

Dear All,

I use

fix 2 all nve

fix 3 all temp/berendsen 4000 0 100

run 2000000

to simulate a cooling process with lammps. A I know, the cooling rate
depends how long the time I run the simulation.

Thus, if the temperature decreases from 4000k to 0K in 400ps, the fooling
rate will be 40K/ps, while running in 2000ps, the cooling rate would be
2k/ps, right?

no. you are discounting the fact, that the berendsen
thermostat is approximating the temperature decrease
with an exponential decay using a time constant
(100 in your case). the smaller this time constant,
the closer the cooling is to your desired linear
temperature decrease.

But, from the output file, I found that after 400ps, the temperature just
decreased to 2000K, not 0K. It means the cooling process did not finish.

are you by any chance running in metal units?
then the 100 of the berendsen time constant would be
100ps, which is fairly long considering your total
simulation time and would explain the behavior you see.

axel.