Equations of state of crystals with strong sixth-order anharmonicity

In a nonsymmetrized approximation of a self-consistent field, the equations of state of densely packed crystals with strong anharmonicity of up to sixth order are considered. These equations include two coefficients which are implicit functions of two dimensionless combinations of the temperature and force parameters of second, fourth, and sixth order. The properties of these functions are investigated; their values are tabulated for broad ranges of variation of the arguments. In particular, it follows from these properties that, as the temperature is reduced, sixth-order anharmonicity is first switched off, and the equations pass over into the already studied equations of state of crystals with strong fourth-order anharmonicity, which is switched off at still lower temperature. The method of obtaining corrections to the given approximation is also considered. © 1980 Plenum Publishing Corporation.