The Electronic Structure And Optical Properties Of （Mg,Fe）SiO₃ Perovskite At Pressure Conditions Of The Earth’s Lower Mantle

(Mg, Fe)Si O₃ perovskite is a main mineral in the Earth’s lower mantle. It is important to explore its physical properties at high pressure conditions of the Earth’s lower mantle. In recent years, the radiative thermal conductivity of（Mg, Fe）Si O₃ perovskite has become a key topic in the high pressure science. In order to obtain the information in radiative thermal conductivity of the lower mantle, the optical-absorption spectrum and refractive-index data at the lower-mantle conditions are needed. The electronic structure and optical properties of(Mg_0.875,Fe_0.125)Si O₃ perovskite crystal at high pressure conditions of the Earth’s lower mantle are studied by the first-principles calculations.This thesis consists of four chapters. The research background and significance,research status, problems to be solved and the main contents of this thesis are introduced in Chapter 1. The basic theory of the first-principles and the software are introduced in Chapter 2. The electronic structure and optical properties of（Mg0.875,Fe0.125）Si O₃ perovskite crystal under high pressures are calculated in Chapter 3. The summary of the full text and the prospects of the follow-up work are in Chapter 4.In this thesis, the main contents and results are as follows:1) Based upon the density functional theory, the optical-absorption spectrum of(Mg_0.875,Fe_0.125)Si O₃ perovskite crystal at high pressure has been calculated by the first-principles. The optical-absorption data show that the spin transition of the ferrous iron has great contribution to cause a decrease in intensity of the absorption band. The results support the conclusion that the spin transition of the ferrous iron from high-spin to intermediate-spin is presence.2) The refractive index of(Mg_0.875,Fe_0.125)Si O₃ perovskite crystal at high pressure has been calculated. The results show that the refractive index is reduced withincreasing pressure and slightly increased with wavenumber in the near-infrared and visible spectral ranges. Therefore, the factor that the refractive index is changed by pressure and wavenumber should be considered.3) The reflectivity and loss function of(Mg_0.875,Fe_0.125)Si O₃ perovskite crystal at high pressure have been calculated. The results show that the pressure is an important factor to change the reflectivity and loss function, the spin transition has slightly influence on them.4) The electronic structure of(Mg_0.875,Fe_0.125)Si O₃ perovskite crystal at high pressure has been calculated. The density of state and electronic density difference data show that the spin transition of the ferrous iron has significant impact on the electronic structure.