Pavlov Y. Calculations of interatomic interaction potential and interatomic correlations in crystals with using the pseudopotentials

The thesis is dedicated to development of the electronic theory of interatomic correlation below the order-disorder phase transition temperature. It is based on description of interatomic interaction that is the determinative factor of the ordering in alloys. The system of analytical equations for equilibrium values of the set of ordering parameters as a function of temperature, concentration, and interatomic interaction between components of alloy is solved. The dependency of ordering energy as a function of distance on the basis of combination of effective pair interactions between components is calculated for Ni0.89Cr0.11 alloy. The effective pair interaction is described by two components: ion attraction by interaction with free electrons, and coulomb interaction of ion frames. The effective pair interaction of crystalline metallic alloy is calculated by means of the pseudopotentials model. The near order parameters are calculated on the basis of the dependency of ordering energy as a function of distance in the ring approach, which is behind the Krivoglaz-Clapp-Moss approach. The contribution of many-particle correlations in Ni0.89Cr0.11 alloy is shown to be small. The temperature dependencies of equilibrium values of the near order parameter at the first coordination sphere and with temperature dependencies of equilibrium values of the long order parameter are obtained using the set of pair correlation parameters and long order parameter. The possible existence of the ordered structure Ni2Cr in Ni0.89Cr0.11 alloy below 700К is theoretically shown. The results of calculations of efficient interatomic interactions are applied for estimation of energy barriers between YBa2Cu3O6 and YBa2Cu3O7 structures, and between cubic and hexagonal modifications of silicon carbide. The effective pair interatomic interaction for silicon, carbon and oxygen was calculated with using the non-conserving Bashlet-Haman-Shuter pseudopotentials. The model of the oxygen ordering with estimation of contribution to free energyofentropy member is proposed for superconductive ceramics. The calculations of 3С and 2Н energy modifications of the carbide silicon are carried out and suggestions about possible mechanism of the structure transformation are made.