Metal Aluminum, Copper, Platinum And Lithium High-pressure Physical Properties Of The Ab Initio Calculations

Ab initio methods are used widely to deduce the data of a certain state of a material from the ones of Hugoniot state or hydrostatic pressure state. Furthermore, using ab initio methods and some approximation of lattice vibration, a complete equation of state of the material can be build up. But it is unfortunately that these methods, when being used to calculate the thermal properties of some materials at high pressure, are either too inaccurate or too intensive in computation. The aim of this thesis is to propose a set of methods which can be used to compute efficiently the thermal properties of the typical metal crystal.The core of the set of methods proposed here is a pair-potential-based mean filed approximation to the ion vibration. In this model, the partition function is factored by neglecting atomic correlations. An atom is displaced in its Wigner-Seitz cell in the potential field of all the other atoms fixed at their equilibrium positions, i.e., the ideal, static lattice except for the wanderer atom. The potential field can be constructed by the effective pair potential which calculated from the first principle. The partition function is simply a product of identical functions for all the atoms, involving an integral of Boltzmann factor over the position of a single atom inside the Wigner-Seitz cell. Using this model combined with the first principle, the thermal properties can be computed.Thermal properties of the face-centered-cubic (f.c.c.) aluminum (Al), copper (Cu) and Platinum (Pt) crystal including the linear thermal expansion coefficient, specific heat at constant volume, Hugoniot in the P-V plane, thermodynamic Gruneisen parameter and elastic constants have been evaluated by using the set of methods proposed here. The calculated properties are in good agreement with available static and shock-wave experimental measurements. Meanwhile, the phase transition of lithium at zero temperature and high pressure is studied as a start point to its thermal properties. The cI16 structure of Li first found by Hanfland et.al is found to be not stabler than f.c.c. at high pressure and maybe do not exist.