Crystal Field -AS_z^2 Does Not Produce One-Phonon Transitions With Delta S_z=+-2 [Comment on EPL 46, 692 (1999) by Leuenberger and Loss]

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.