Diffusivity in LAMMPS

Hi,

I am currently working on a system where I need to find the diffusivity of A in an ionic mixture of (A+B+C). How can I fix the MSD for estimating diffusivity in LAMMPS. It was not clearly mentioned in the manual. Please give some suggestions on grouping.

Thanking you.

with regards
K.RAKESH.

See the group command for assigning A atoms to a group.
See the compute msd command for calculating the MSD of
a group of atoms.

Steve