Elastic properties of the (001) face of xenon crystals

Abstract

In this work we investigated the elastic properties of the (001) face of xenon crystal. The slabs (twodimensional crystals) defined by (001) planes are generated, their structures are optimized and the slabs thermodynamic functions in excess to the crystal bulk calculated. The calculations are based on the Lennard-Jones 6−12 force field, classical elasticity theory and surface thermodynamics. In this work, the number of planes undergoing relaxation is not a priori constrained but it follows from the minimization of the free energy of the slabs and of the bulk, in respect to atomic positions. The value of the surface free energy is calculated as a function of the homogeneous strain of the 2D (001) cell measured relatively to the cell of the stable 3D crystal. At 0 K, when strain is not applied, the specific surface free energy is about 0.064 Jm^-2 and decreases by about 6% at 50 K. The surface stress is positive amounting to 0.010 Jm^-2 at 0 K, and it decreases by about 50% at 50 K. We find that the surface stress can be released by a reorganization of the interatomic distances at the crystal surfaces. The surface excess mean value of the slab elastic constants at 0 K is small (0.012 GPa) and it decreases by about 35% at 50 K. The method proposed can be alternative to molecular dynamics simulations in order to assess the excess surface properties of materials having a complex structure.