Contribution of concerted exchange to the entropy of self-diffusion in Si

The concerted-exchange (CE) mechanism is at present the only viable candidate for atomic exchange that does not involve intrinsic lattice defects. In order to evaluate its contribution to self-diffusion in Si, we calculate the entropy associated with CE. We include full relaxation of the energy surface through an interatomic potential and take into account the dominant contributions of vibrational modes through the harmonic approximation. This gives an entropy of 6.3kB, which accounts for a large portion of the experimental result (7kB--9kB). We conclude that the CE mechanism is a significant contributor to self-diffusion in Si.