how to control temp. in initial steps

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1

Dear lammps users

I am trying to perform an NVT simulation on a box of some CO2 molecules using a reaxFF forcefield. The problem is that in initial steps the temperature is so high, about 5000K, which cause the CO2 molecules to be degraded. The input file is:

some comments

dimension 3
boundary p p p
units real
atom_style charge
read_data data.30CO2_min

pair_style reax/c NULL
pair_coeff * * ffield.kowalik C O
neighbor 2.0 bin
neigh_modify every 10 delay 0 check no

timestep 0.5
fix 1 all nve
fix 2 all qeq/reax 1 0.0 10.0 1.0e-6 reax/c
fix 3 all temp/berendsen 30.0 300.0 100.0

dump 1 all atom 5 30CO2.lammpstrj

thermo 5
run 10000

Now my question is, how I can control the temperature in the initial steps?

Thanks in advance, I appreciate your help
Hossein Hajiabadi
Nikopardazesh Inc.

2

Dear lammps users

[…]

Now my question is, how I can control the temperature in the initial steps?

that is the wrong question! what you should ask yourself is: why does the temperature rise that much?
“controlling” the temperature will suppress the problem. that is no scientific solution. you will have to understand what the problem is and eliminate it.

most common causes are bad simulation settings (timestep too large, too infrequent neighborlist updates, wrong units) or bad/unsuitable force field parameter or bad geometry (for atoms or simulation cell). neither of those can be “cured” by “controlling” the temperature.

axel.

3

Dear Axel

Thank you for your clarification. now I have realized that the forcefield parameters cause the problem!

Sincerely