Combined Electronic Structure Theory of Relativity, quasi-degeneracy, and Electron Correlation Oriented Towards Electric and Magnetic phenomena in molecules

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In this research project, we developed the electronic structure theories and methods which can applied to quasi-degenerate systems, relativistic and dynamic electron-correlation problems, and executed some fundamental researches of molecularproperties in electric and magnetic substances.Ten-no developed a four-component relativistic MP2-F12 method to treat molecules with heavy elements accurately. He investigated the short-range behavior of electrons based on the direct perturbation theory and applied a kinetically-balanced relativistic geminal basis to multi-electronic systems for the first time. Furthermore, Ten-no proposed a new quantum Monte Carlo (QMC) method to treat quasi-degenerate and excited sates of strongly correlated systems. He developed the model space QMC (MSQMC) method to determine an effective Hamiltonian stochastically. MSQMC transcends the limitation of the standard ab initio methods.Nakano developed the relativistic occupation restricted multiple active space multi … More configuratoinal self-consistent field method (ORMAS-SCF) method and second-order perturbation theory based on it. He applied them to the excited states of rear-earth and transition metal compounds as model complexes of magnetic or electroluminescentmaterials. He also made a systematic investigation on the effect of the negative energy spinors in order to estimate the methods including the highly relativistic effects.Hada combined the many-electron Infinite-order Douglas-Kroll-Hess ()IODKH) method with the SAC-CI method which is an accurate electronic structure method for excited states. He applied this method to molecular magnetic properties of heavy-metal complexes.Yanai developed ab initio density matrix renormalization group (DMRG) method to achieve high accuracy electronic structure calculations for molecular systems containing heavy elements. As its practical application, the DMRG method was applied for the study of the electronic structures of multi-nuclear transition metal complexes. Our calculations provided detailed theoretical analysis of oxidation states of metal sites where there are considerable difficulties in interpreting experimental observations. In addition, the method to incorporate the spin-orbit effects, typically arising in heavy metal systems, into the DMRG wave function was developed. Less