Hi, to who use lammps:

How to compute the relaxtion time of fix langevin commmand?

But why is

hi @ILEILEILE,

The damp parameter is the Langevin caracteristic time and is directly involved in the computation of the friction force which replace actual solvent effect. Short time = high friction = high viscosity. More details are given in the manual just below the equation you copied.

Please see any detailed computation of Langevin equations (example here) to see how you can rewrite the equations so that the relation between \lambda, \tau (or damp) and m becomes obvious.