  Recently Leuenbeger and Loss suggested a theory of phonon-assisted relaxation
in a molecular nanomagnet Mn-12 that "contrary to previous results is in
reasonably good agreement ... with all experimental parameter values known so
far". The purpose of this Comment is to show that the model of Leuenberger and
Loss and its comparison with experiment are premised upon their incorrect use
of the linear formula for the strain tensor. The spin-phonon coupling
introduced by Leuenberger and Loss disappears if the nonlinear term in the
strain tensor is taken into account.
