A First Principle Study Of The Physical Properties Of Materials Under Extreme Conditions Of Metals And Metal Hydrides

In this thesis, we perform first-principles approach to calculate the thermodynamic properties metals and their hydrides under high pressure and analysize the electronic structure, phonon spectrum, the thermal properties, electrical properties and thermal neutron scattering. The thesis has been divided into the following parts:In Chapter 1, we briefly introduce the development of experimental research and theoretieal simulation method about the materials under extreme conditions.High pressure equation of state of the metal and their hydrides are very important in social life and national defense.In Chapter 2, we mainly introduce the density functional theory (DFT) as well as the theories of correlate electron and dynamical mean field theory(DMFT), which are our theoretical foundation and computational implementation to deal with the issues discussed in this thesis.In Chapter 3, Hydrogen and deuterium are the most simple and abundant elements in the Universe.The behaviors of hydrogen and deuterium at high pressures are the subject of intense study not only because high-pressure studies of hydrogen are relevant to our understanding the physics and chemistry of planetary interiors, but also because it is a central input in study of inertial confinement fusion (ICF) and nuclear weapons.This work is devoted to investigate systematically the cold energy and pressure of hydrogen and deuterium under extreme conditions with numerical simulation.A detailed comparison is also discussed between the results of various theoretical models,other theoretical data and available experimental data. It can be proved the suitable and stability of pseudopodential method under extreme conditions and verified the validity of theoretical models.The cold energy and pressure of pure fcc copper, aluminum also have been calculated by using first principles base on desity functional theory whin the pseudopotential plane-wave method.The calculation results show the different exchange-correlation potential affects greatly the cold energy and pressure of fcc metals.Our work suggested that the choice of pseudopotential function plays an important role in Investigation of materials under high pressure.In Chapter 4,the equation of states and the thermal properties of multiphase tin (Sn) have been calculated by using first principles hase on desity functional theory whin the pseudopotential plane-wave method. We analysised the lattice parameter,bulk modulus and enthalpy in different structure. A detailed comparison with available experimental data and other theoretical data is also performed. LDA results are in better global agreement with experiment than the results of GGA.The temperature and the pressure dependent thermodynamic quantities, such as the entropy, and the Gibbs free energy, are estimated by employing the phonon density of states, which is calculated by using the frozen phonon approximation.We perform first-principles simulations to calculate the thermal properties and phase transformation of tin.In Chapter 5, we have performed QMD simulations to study the thermophysical properties of tungsten under extreme conditions, the equation of states,electrical and optical properties of expanded tungsten under extreme conditions are investigate.The thermodynamic properties of the expanded fluid tungsten at density from 2 to 18 times lower than the normal solid density have been studied. It is found that the conducting electrons become localized at lower densities.In addition, the negative derivative of the electrical resistivity on temperature at the relative volume 5-6 lower than the normal solid density demonstrates that the metal to nonmetal transition is observed in the expanded tungsten.In Chapter 6,the theories of correlate electron,dynamical mean field theory (DMFT) and Quantum Monte Carlo have been reviewed.Physical models and descriptions of the continuous-time quantum Monte Carlo algorithms are presented in enough detail.It has been improved understanding of the half-filled Hubbard model metal-insulator transition by single-site dynamical mean field theory.And we also discussed the parallel performance of the continuous-time quantum Monte Carlo algorithms.Also we perform LDA+DMFT simulation to calculate the properities of Cerium,and it seems that LDA+DMFT results are in better agreement with experimental than the results of conventional LDA(GGA).In Chapter 7, the electronic structure and properties of plutonium hydrides' bulk and (111) surface are studied using the first principles projector augmented wave (PAW) method. The LDA (GGA)+U schemes has been used to account for the strong on-site coulomb repulsion among the localized Pu 5f electrons. We discuss how the choice of U as well as the choice of exchange-correlation potential affect those properties. Calculation results show that the pure LDA or GGA fails to give the accurate lattice parameter and proper electronic structure compared with experiments, while the LDA+U schemes can effectively remedy these failures.In Chapter 8. the electronic structure and properties of uranium hydride and deuteride under pressure are investigated within the DFT and DFT+U formalisms. We also utilize DFT and DFT+U to analysis of the magnetic properties by comparison of the thermodynamic properties,the magnetovolumetric structure and consideration of the crystallographic differences under pressure between the two phases. Such questions are an instance of the more general topic of correlation sensitivity for other actinide elements.In Chapter 9, Frequency distributions of 7Li and 1H bound in 7LiH are calculated by first-principles with frozen-phonon approach.Based on the theory of thermal neutron scattering, we produce thermal scattering law data. Finally the thermal scattering law data of 7LiH are used in a simplified fusion source model to analysis the inside neutron flux.