question about group dynamic

Dear all

I would try this first by writing logic like:

run N
define the group you want
velocity command on the group
run N

If you can get that to work, then you could put
the commands into a loop. Or perhaps you
could use them with the “run every” option of
the run command.

To define the group you want (random subset of
another group), I suggest you look at atom-style
variables. There is a random # generator, and
a group operator (select atoms in a group), so
you can write a boolean atom-style variable
that selects a random subset. The group command
lets you clear an existing group and assign again
to it using the group variable option.


Dear Steve
Thanks a lot

I will try what you suggest and keep you informed.
More precisely, I wish to select randomly one atom in a defined group, change its velocity at this time, and repeat such an event every N timesteps. So I will apply the velocity for each selected atoms only once. These atoms with new velocities will interact with other atoms in the simulation box until end of the simulation.