Studies on Electronic Structure of p Electron Systems and Nanostructure Materials Based on First-Prinsiples Methods for Strongly Correlated Electrons

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The goal of this project is to develop a hybrid computational method for electronic structure calculations of strongly correlated electron systems by combining the density functional theory and solvers for models of strongly correlated lattice models. By establishing the method, we apply it to p electron systems and nanostructure materials. This hybrid method consists of the following three procedures: (1) Calculate global electronic band structure by the density functional theory using the local density approximation and GW approximation (2) Eliminate and trace out the high-energy scale by downfolding and derive low-energy effective models (3) Solve the low-energy models by reliable low-energy solvers. This scheme has been applied to Sr2VO4. We have revealed that Sr2VO4 is near the metal-insulator phase boundary with antiferromagnetic order and shows complicated spin-orbital orders. Next we have applied to electronic structure calculation of YVO3. It shows the insulating ground state … More with the gap given by 0.9 eV, which is in agreement with the experimental gap, 1.0eV. Based on these successful results, we have applied this scheme to p-electron systems. In p-electron systems, we have employed the plane-wave basis. This has been applied to an organic conductor, BEDT-TTF compound and we have derived the low-energy effective Hamiltonian. We have also examined the efficiency for excitation spectra. The downfolding scheme has been applied to GaAs and LiF and the optical conductivity has been calculated. These results show that excitonic effects are correctly captured by this scheme. In this project, several different types of low-energy solvers have also been developed. In addition to the path integral renormalization group, Gaussian basis Monte Carlo and improved variational Monte Cairo methods have been developed and we have clarified that these method may be used as a highly accurate low-energy solver essentially without the minus sign problem. By these achievements, a new type of electronic structure calculation method based on the three-stage scheme for strongly correlated electron systems including p-electron compounds are now well established. Less