Velocity Create Error during Setup

the methane group has only one particle? there is no such thing as the temperature of a single particle.

You could draw a single velocity from the MB distribution that corresponds to that temperature, though. Nice catch with the group command, though.

Velencia - your mof5 group contains only 7 atoms (IDs 1 to 7) and your methane group contains only a single atom (ID 8) - is the the behaviour you wanted?

I agree with the comments about ambiguity in the “temperature” of one atom.

But the reason LAMMPS is giving an error is b/c when it computes the

temperature of a group of atoms it subtracts 3 degrees of freedom by default

(for the center-of-mass motion). For one atom, you thus have a group with
no DOF. You can do this instead:

group one id 1
compute foo one temp
compute_modify foo extra 0
velocity one create 300.0 49264 temp foo mom no

and LAMMPS will not complain.

This is using the “foo” temperature compute (with no DOF subtracted, 3 is the default),

to init the vel of the atom. You also need to not zero the linear momentum
since for one atom, it would reset the vels to 0.0
before rescaling them to the chosen temp and you’d get the same error as before.