SURFACE THERMODYNAMIC FUNCTIONS FOR NOBLE-GAS CRYSTALS

Surface thermodynamic quantities have been calculated as functions of temperature between 0°K and the melting temperature for the (111), (100), and (110) surfaces of the noble-gas solids Ne, Ar, Kr, and Xe. The method of calculation differs from the methods used in previous treatments of surface thermo-dynamic functions in that the atomic vibrations are taken into account, and the vibrational frequencies are properly calculated rather than obtained from a Debye model or an Einstein model. The quantities calculated are the static surface energy, vibrational surface energy, surface entropy, vibrational surface free energy, and surface specific heat. In addition, a surface frequency-distribution function f8(ia) has been calculated;f 8(ω) is positive at low frequencies, because of the presence of surface modes of vibration, and negative at higher frequencies. This behavior of f8(ω) produces a narrow peak in the graph of the surface specific heat as a function of temperature.