An investigation was made of the temperature dependence of the activation free energy for the atomic diffusion in the face-centered cubic Lennard-Jones system within the transition states theory based on the quasi-harmonic approximation. The activation free energy consists of the static activation energy and the vibrational free energy difference between the saddle point and the equilibrium state, and it was shown that both of them strongly depend on the system volume and the temperature. The temperature dependencies of both quantities exhibit opposite tendencies, i.e., the static activation energy decreases, while the free energy difference increases with increasing temperature. As a result, the activation free energy exhibited a weak temperature dependency. The effects of anharmonicity upon the activation free energy were investigated by comparing the activation free energies obtained using the quasi-harmonic and harmonic approximations.

Theoretical Calculation of Activation Free Energy for Self-Diffusion in Prototype Crystal. K.Sato, S.Takizawa, T.Mohri: Materials Transactions, 2010, 51[9], 1521-5