The entropy of migration signifies the alteration in lattice vibrations that accompany the displacement of the jumping atom from its equilibrium state to the saddle point configuration. In the Vineyard approach, the probability of reaching the transition state is derived by comparing the configurational partition functions of the initial state and the transition state, while the rate of crossing is determined by the one-way forward flux at the transition state. The expression for the migration entropy, in harmonic approximation, is therefore given by: