Free Energies of Molecular Crystal Surfaces by Computer Simulation: Application to Tetrathiophene

We describe a general simulation protocol for the evaluation of the surface free energies of molecular crystals, which are of broad interest for phenomena such as polymorphism and crystal growth. The method has been applied to selected surfaces of two polymorphs of tetrathiophene. The simulations highlight an important temperature-dependent entropic contribution to the surface free energies, which is not included in widely used static simulations of surface structure and energetics.