New methods for electronic excited states of solids using localized basis

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We have developed a first-principles method for excited states of polymers using gaussian basis sets and proposed other efficient methods for studying excited states of solids, as summarized as the following.1.A computational method has been developed to calculate excited states of one-dimensional periodic systems using Hartree-Fock crystal orbital theory with gaussian basis sets, coupled-cluster theory, and equation-of-motion coupled-cluster theory. The method makes it possible to calculate excited states of polymers by taking electron correlation effects into accounts with high accuracy. The calculated excitation energies of polyethylene were well comparable with experiments.2.Two spin-density wave states were found in polydiacetylene between acetylene and butatriene structures from spin-unrestricted density functional calculations. The corresponding potential energy functions were different.3.A simplified computational method for excited states was proposed using time-dependent density functional theory and Bethe-Salpeter equation based on the assumption of a local electron-hole interaction.4.A computational method for excited states of strongly-correlated materials was proposed using dynamical mean-field theory and GW approximation. The method was successfully applied to electronic band structure of Ni. The agreement with the experimental band energies was excellent.5.Exchange-correlation kernel (fxc) in time-dependent density-functional theory was obtained from two-dimensional Hubbard model. By comparison with theoretical excitation spectrum it was demonstrated that fxc has strong energy dependence in the energy regions where there are many-body excitations.