quench the system

Dear lammps users,

I am using langevin thermostat to quench the system from 600 K to 300K in real unit. But looking at the temperature in the log.lammps file, I found that temprature decreasing from T around 150 to 50 which is totally different from what I had expected.

Here is the command I am using.

fix 12a freeions langevin 600 300 100 904297

I also attached the code and the input file.

I really appreciate any help.

Thanks in advance,

Shahzad

in.simple (3.18 KB)

initial (21.4 KB)

First of all, the restart file is so old that I can’t even run it with a recent LAMMPS version.

By examining the input script, atoms of type 3, or those in the group freeions, are the only ones applied with a fix and hence the only atoms that are moving. However the thermo output is applied to all so it is expected that the temperature of the system that contains immobile atoms does not equal to the temperature of the group freeions.

You would need to define a fix ave/time that applies only to group freeions to estimate its temperature.

Cheers,
Ray

Hi Ray,

Thanks for your quick reply! Actually I am running the files with this version “lammps-14Mar13”! But I attached a new input file.

I checked what you recommend. You are right! By outputting the temperature of freeions, I found that it is changing from 600K to 300k.
I don’t understand the explanation though, other ions are fixed and don’t have any contribution to the kinetic energy and therefore the temperature of the system?!

Shahzad

tsimp.txt (10.6 KB)

in.simple (3.18 KB)

I checked what you recommend. You are right! By outputting the temperature of freeions, I found that it is changing from 600K to 300k.
I don’t understand the explanation though, other ions are fixed and don’t have any contribution to the kinetic energy and

Of course. Atoms that do not move do not have any kinetic energy and hence do not have any contribution to the global temperature. Therefore the global temperature will be much lower when the system temperature is estimated by including kinetic energies from all atoms (when some atoms are immobilized).

Cheers,
Ray