THE MICROSCOPIC THEORY OF THE SURFACE-PROPERTIES OF ANHARMONIC CRYSTALS .1. GENERAL-METHOD AND (001) SURFACE OF BCC CRYSTAL

The self-consistent theory of the structural, dynamical, and thermodynamic surface properties of anharmonic crystals previously given for one- and two-dimensional models is extended to the surfaces of three-dimensional crystals which take into account the surface anisotropy. After considering the reference system, in the general case, the equations for the properties of the interface cyrstal-vapour to the second order in the temperature are derived. The (001) face of the BCC crystal is investigated. The lattice relaxation and dynamics are calculated. The surface Helmholtz free energy and other thermodynamic properties are obtained. At high temperatures, the surface specific heat increases linearly with temperature due to the anharmonicity.