The Study On Electronic Excited States And Image-potential States Of Surfaces

Electronic excited state and its excitation spectra properties of the system plays an important role in physics and chemistry.Therefore,an in-depth understanding and accurate calculation of electronic excited states are of great significance.Based on density functional theory(DFT)within the local-density approximation(LDA),use of the many-body perturbation theory within the GW approximation(GWA)is made to calculate the quasiparticle band structures of bulk MgS and LiCl.Taking the electron-hole interaction into consideration and solving the Bethe-Salpeter equations(called BS equations for short),the optical absorption spectra of bulk MgS and LiCl are further evaluated.Using the many-body perturbation theory within the GW,the quasiparticle band structures for the surfaces of alkali metal halides including LiF(001)-(1X1),LiCl(001)-(1X1),LiBr(001)-(1X1)and LiI(001)-(1X1)are investigated systematically.Since the GWA improves the electronic exchange-correlation within the LDA,the obtained GWA band gaps are in good agreement with the corresponding experimental results.It is found that the surfaces of LiF(001)-(1X1),LiCl(001)-(1X1),and LiBr(001)-(1X1)have negative electron affinity,the image-potential state exists in the vacuum outside the surface,which results from the electrostatic interaction between an electron outside the surface and the polarizability in the insulator.The distributions of the wave functions for the image-potential states along the directions perpendicular to the surfaces are investigated,the calculated local potentials using the GWA are compared with the corresponding classical image potentials.However,LiI(001)is not a negative electron affinity surface and therefore there is no image-potential state in the vacuum outside the LiI(001)surface.This thesis is divided into four chapters.In the first chapter,the first principles calculation method is expounded systematically,from the Born-Oppenheimer approximation,the density functional theory to many-body perturbation theory.The second chapter introduces the theory of the image-potential states involved in this thesis.The third chapter briefly introduces the contents and achievements of my postgraduate work.The fourth chapter gives a summary of my wholeresearch work and shows the important results and remaining questions of the research.The future research work is also prospected in the fourth chapter.