Electronic Excitations Of Li Halides From Many-body Perturbation Theory

Electronic excited state and its excitation spectra properties of system plays an important role,Therefore, an in-depth understanding and precise calculation of electronic excited state are of greatsignificance. A large amount of calculation show that the density functional theory (DFT)(LDAand GGA) can calculate the geometrical structure of a system at the ground state accurately.However，it cannot describe the electronic excited state of semiconductor and insulators, becauseit usually underestimates the energy gap of insulators and semiconductors seriously. The many-body perturbation theory can be applied to single electron excited states. Within this many-bodyperturbation theory, calculation results of density functional theory is treated as a zero-orderapproximation. By introducing GW corrections, quasiparticle band structure can be calculated.Optical excitation is affected by electron-hole interaction. Solving the Bethe-Salpeter equation withmany-body perturbation theory, we can calculate optical absorption spectra.There are three chapters in this thesis. The first chapter describes first principles calculationmethod (including the density functional theory and many-body perturbation theory) briefly. Thesecond chapter introduces the main work. We present the quasiparticle band structures, the opticalexcitation spectra and the excition wave functions of bulk LiCl and LiBr using many-bodyperturbation theory. The calculated band gaps and the optical absorption spectra are in goodagreement with experimental data. Some outlooks of our work are given in the third chapter.