Vibrational Entropy in Static Simulations of Point Defects

A new procedure for computing the vibrational entropy in point defect simulations is presented. The method rests on including in the calculations all the atoms whose frequencies are influenced by the defect field. This development is motivated by the failure of the previous graphical extrapolation method when applied to crystallite sizes accessible to nowadays hardware. The analysis carried out here also provides a consistent dilation coefficient to use, e.g., for correcting entropies from fixed volume to fixed pressure calculations, while performing static simulations, strictly valid at 0 K. Any semiempirical interatomic potential currently in use should be able to benefit from this technique.