Can "fix" command implement in molecule id style?

Hi lammps users,

Is there any way to implement "fix command " something in “molecule id” style not the “group id” style? Just like the form:

fix ID molecule ID style args

The reason is because I have 50 molecule in the box, and I want them to be vibrational equilibrium (by removing translational and rotational velocities of each molecule). To do this, I can do following operation:

group group_1 molecule 1

group group_2 molecule 2

group group_50 molecule 50

fix 1 group_1 momentum 100 linear 1 1 1 angular

fix 2 group_2 momentum 100 linear 1 1 1 angular

fix 50 group_50 momentum 100 linear 1 1 1 angular

Then, each of molecule’s translational and rotational velocities will be removed. However, there is a limit (32) for group numbers, and I know it is very difficult to extend max group number after search on LAMMPS Mailing Archives.

I am wondering if I can only fix is in molecule ID style by LAMMPS or by minor changes? Or I can do this with other way?Otherwise I should write a total new fix, with will difficult without using “group” class.

Thank you in advance.

Jiang Xiao