Ordering Phenomena in Transition Metal Oxides

Electronic structure calculation with new tools for realistic correlated electron systems   

Electronic structure calculation with new tools for realistic correlated electron systems A computational method for electronic structure of correlated electron systems is presented. The path-integral renormalization group (PIRG) method is combined with the formalism of density functional theory to allow accurate determination of the low-energy properties of strongly correlated electrons. This formalism makes it possible to incorporate the realistic band structure derived from the first-principle calculation together with an estimate of the screened interaction for the bands near the Fermi level. The PIRG method allows to take into account temporal and spatial quantum fluctuations in the low-energy level after the downfolding of the high-energy electrons. As an example, the formalism is applied to a couple of transition metal compounds such as Sr₂VO₄. The LDA calculation of this compound predicts the insulating behaviour while the Hartree-Fock theory concludes the spin-orbital ordered insulator. The present method allows a precise determination of the electronic structure beyond these approximations by taking into account the dynamical and short-ranged fluctuations. The present new scheme opens a way to study strongly correlated electron systems.