The Excited State And Its Time Evolution Of CO Molecules Adsorbed On The Surfaces Of Insulator Materials With Wide Band Gap

Excited electronic state and spectral properties plays an important role in materials science.It is of great significance to understand excited electronic state deeply and systematically,calculate excited electronic state rapidly and accurately,and predict excited electronic state timely and effectively.For the discussion of the electronic ground state properties of a many-body system,the density functional theory(DFT)within the local density approximation(LDA)or generalized gradient approximation(GGA)is accepted by scholars and applied to the study of adsorption on solid materials surfaces.Using the LDA or GGA,the geometrical structure of the ground state and the single electron wave function can be calculated accurately.However,for insulators and semiconductors,the energy gaps obtained within the LDA or GGA are apparently smaller than experimental results.Excited electronic states,which includes the quasi-particle excited states and the electron-hole excited states,can be described by many-body perturbation theory(MBPT).Within the MBPT,the GW approximation(GWA)is used to improve the treatment of electron exchange and correlations within the LDA or GGA.The quasi-particle band structure can be calculated accurately using GWA.The electron-hole excited states can be described systematically by the two-particle Green's function theory,in which the electron-hole interaction is taken into consideration.The optical absorption spectra and reflectivity spectra can be obtained accurately by solving the Bethe-Salpeter equation(BSE).For a coupled system with small molecules adsorbed on the substrate surface,the time-dependent Schroedinger equation for the effective Hamiltonian of two particles may be used to describe the time evolution characteristic and life time of the molecular exciton state accurately.This paper is composed of four parts.In the first part,the first principles calculation method is expounded systematically,from the choice of pseudo potential,the density functional theory to the many-body perturbation theory.The second part introduces the theoretical methods applied in the study for this thesis.The third part briefly introduces results of my postgraduate work.The whole research work is based on DFT and MBPT.The quasi-particle band structure,optical absorption spectra and reflectance spectra of Ba S are calculated.Then,I have also studied the quasi-particle band structure and optical absorption spectrum of the CO: Li Cl(001)-(1X1)surface as well as the time evolution of the molecular exciton state.In the fourth portion,I sum up the whole research work and point out the innovation and deficiency in the research.The outlook of the research work is also presented finally.