Entropy of point defects calculated within periodic boundary conditions

A possibility to calculate both the entropies of formation and migration of point defects in semiconductors is presented. Knowledge of the entropic contributions is especially important for the correct description of high-temperature processes like growth or annealing. Using the self-consistent charge density-functional based tight-binding method (SCC-DFTB) we have calculated the predominant part of the entropy, resulting from lattice vibrations. Strong finite-size effects have been observed while investigating the formation entropies of isolated vacancies in diamond and silicon. We demonstrate how these problems can be overcome with the help of linear elasticity theory.