Electronic Structure Calculations
In electronic structure calculations, one of the most successful approaches for studying the electronic and stuctural properies of condensed-matter systems consisting of electrons and ions is based on the pseudopotential method in the framework of the local-density-functional approximation, in which the electronic orbitals are expanded in plane wave basis functions. For latge systems, however, this approach requires a large number of plane waves and many claculational difficulties arise. To solve these difficulties, a real-pace calculational technique is under development, which employs discretized grids in real space to solve the Kohn-Sham equation and enables us to perform large scale electronic structure calculations, with use of massively parallelized supercomputors. This method is coupled to the Car-Parrinellomolecular dynamics simulation technique to describe the dynamical aspect such as melting, phase transition, annealing and quenching effetsm and time evolution of ion motions. The molecular dynamics simulations based on the embedden atiom potential liquid melting and shock Hugoniot structureal phase transition and amorphization of crystalline Si. This technique is being used for studying the electronic structure and the transport behavior of carbon nanotubes.
Dielectric Matrix and Response Function
The full dielectric matrix, which includes crystal potential, local-field, exchange- correlation effects, is calculated using the pseudopotential method The calculational method based on the real spacs formalism is under development, which requires advanced numerical techniques for Green's function, susceptibility, and anlytical continuation. The dielectrix matrix approach has been used for the calculations of plasma frequency and optical properties of Li and Al and the electron repulsive parameters(Coulpmb pseudopotential)in Li,Al,Nb,Pd, and PdH. Current studies are performed for the Coulomb pseudo potential parameter of a C36 solid.
Applications to Real Materials
One of the amjor interests in real materials are the defect propertiesof semi-conductors, particlarly, wide-gap semiconductors such as SiC, GaN, and ZnSe, which are promising materials for blue-green laser devices. The atomic model and electronic structure of intrinsic defects and impurities are investigated. In Si, the role of hydrogen and oxydn is being studied, in conjunction with device applications. Adsorption and diffussion of adatioms on Si surfaces are important in the study of growth mechanism. The role of surfactants on epitaxial growths of Si and Ge is also investigated. The real space calculational approach is a very powerful technique for studying clusters and nano-crystals, which give a physical insight to understanding the properties of quantum structures such as quantum dots.