dynamic group and nvt

LAMMPS LAMMPS Mailing List Mirror
1

Hi, All Users and Developers,

I want to use group command with dynamic keyword, and use nvt fix to control the temperature. However, the result is very weird, so I did a simple test.
I only set 6 atoms to group “ch4” in the box. And, set “gas” as a dynamic group which parent-group is ch4. Since I didn’t change the region or insert/delete atoms, the “gas” and “ch4” should be the same, although “gas” is dynamic group. Then, fix nvt (see the input script).
If I use " fix action ch4 nvt temp 300 300 100 ", the result works well.
However, if I use “fix action gas nvt temp 300 300 100”, the result shows that the atoms only have very very small velocity. The nvt seems not working.
Does anyone know where the problem is?
My lammps version: lammps-29Aug14
Thanks!

Tianhao
Peking Univ.

2

I think this is now fixed. There were some issues
with the temperature compute and thermostat updating
their degrees of freedom correctly for dynamic groups.

So please try the patch that will appear later today.

Note that if you define the region for the dynamic group
to be the simulation box, then atoms can move outside
the box before the next reneighbor. That means they

will not be in the dynamic group on certain timesteps.

In that case you are probably better off using a region
that extends beyond the box bounds in one or more
dimensions.

Thanks for posting the test script,
Steve