Interfacial free energy calculations via virtual slip

The computation of a solid-solid interfacial free energy requires the calculation of the work required to form the interface from the perfect crystal along any reversible pathway. The practical difficulty lies in finding a computational path connecting the perfect crystal to the defective crystal that is reversible. We present a method for calculating the interfacial free energy of any solid-solid interface defined geometrically by a slip on a specified crystallographic surface, for example, a stacking fault or an antiphase boundary. A non-physical pathway is defined using a 'virtual slip' of the system in which atoms can exist in two places at once. This avoids any 'hard collisions' between atoms, and assures that the pathway is reversible. This connects the perfect and defective crystals directly, as described by a given interatomic potential, without recourse to any harmonic approximations.