A Study On Mechanical, Electronic, Optical Properties Of GuXSe₂（X=B,AI,Ga,In,TI） By The First-principle Calculations

Crystal structures of material and various physical properties of material are calculated by using first principles. These results provide theoretial guidence and basis for the material design and preparation. In this thesis, mechanical properties, electronic properties and optical properties of CuXSe2(X=B,Al,Ga,In,Tl) crystal structures are calculated based on the density function theory.Firstly, the stability of crystal structures and mechanical properties of CuXSe2(X=B,Al,Ga,In,Tl) have been investigated by first-principles method within the generalized gradient approximation(GGA) and local density approximation(LDA).Lattice constants, bulk modulus, shear modulus, Young’s modulus and poisson’s ratio of CuXSe2(X= B,Al,Ga,In,Tl) are analyzed. According to the standard of crystal mecganical stability, the results show that CuXSe2(X= B,Al,Ga,In,Tl) is mechanically stable at zero temperature and zero pressure. The lattice constants and the compressibility of crystal become larger with ionic radius increasing. Based on pugh empirical relationship, it can be found that the compounds of CuXSe2(X=B,Al,Ga,In,Tl) are ductile materials.Secondly,the electronic properties of CuXSe2(X=B,Al,Ga,In,Tl) have been studied using B3 LYP functional. Band structure, density of states, population analysis of CuXSe2(X=B,Al,Ga,In,Tl) are analyzed. The results indicate that these crystal structures have similar band structure and belong to direct band gap semiconductor. Band gaps of CuXSe2(X=B,Al,Ga,In,Tl) crystal structures are gradually decreasing with the increasing lattice constants. It is found that bonding of B-Se, Al-Se is stronger than bonding of Cu-Se in the CuBSe2, CuAlSe2 component. To CuGaSe2, CuInSe2, CuTlSe2 component, bonding of Cu-Se is stronger than bonding of Ga-Se, In-Se, Tl-Se, which are in good agreement with density of states.Finally, in order to the study of optical properties we investigate the dielectric function, absorption spectra, refractive index, conductivity, energy loss spectroscopy of CuXSe2(X=B,Al,Ga,In,Tl) by first-principles method. The restults show that absorption edge shifts toward low energy direction and have a red shifing phenomenon with the increasing of atomic number. In addition to B, the refractive index increases gradually with atomic number X change. According to the value of light quantum limit of dielectric, It is found that energy range of optical spectrum become narrowing. The biggest energy loss function become smaller. This provides a theoretical basis for the research of photoelectric properties.