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Previously, various symmetry-adapted (SA) and broken-symmetry (BS) computations have been performed for strongly correlated transition metal species so as to examine magnetic properties in simple cluster models such as binuclear transition metal oxides. Though SA computations such as the complete active space configuration interaction and CASSCF are desirable for estimating physical constants, these computations are heavy for larger cluster models with strongly correlated electrons. K[SUB2]NiF[SUB4] is known to be the two-dimensional perovskite-type antiferromagnet and to have the electronic configuration similar to that of La[SUB2]CuO[SUB4]. Here, we have examined the utility and applicability of the BS spin-polarized hybrid-density functional theory (HUDFT) for cluster models of K[SUB2]NiF[SUB4]. As the result, HUDFT calculation such as UB2LYP has provided the reasonable effective exchange integral (J[SUBab]) followed by our approximately spin projected scheme, in comparison to the experimental one. It was also found that the square planar tetranuclear model has provided the most reasonable J[SUBab] value by HUDFT. In addition, external effects such as putting point charges around cluster models and changing distances between nickel and fluorine have been also examined. The natural orbital analysis by HUDFT has been carried out to obtain natural orbitals and their occupation numbers. Charge density, spin density, and chemical indices expressed by the occupation numbers have been also obtained to elucidate the nature of the chemical bonds in the K[SUB2]NiF[SUB4]-type solids. [ABSTRACT FROM AUTHOR]

Many research activities on the solid-state oxide fuel cell (SOFC) have been performed for production of electronic energy without fossil fuel. To design the efficient SOFC electrolyte, we should clarify the detailed mechanism on oxide ion conduction. LaAlO3 perovskite has been much expected as the electrolyte material. It is known that strontium doping at lanthanum site lowers the activation energy for the oxide ion conduction. In this study, we have investigated the mechanism of the activation energy decrease in strontium-doped LaAlO3 by the cluster model calculations based on hybrid density functional theory. It was concluded that the ionic and covalent bonds between counter cation and conductive oxide ion is responsible for the activation energy change. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [ABSTRACT FROM AUTHOR]

Abstract: In the strong correlated perovskite-type copper fluoride of K2CuF4, the degree of freedom in d orbitals of copper cation should be considered to understand the magnetism. We performed the cluster model calculations under consideration of octahedral fluorine anions around copper cation, in order to investigate the magnetism. At the amplitude of Jahn–Teller distortion, the alternate type orbital ordering and the experimental effective exchange integral (Jab ) value were reproduced. The calculated potential energy curves were discussed, from the viewpoint of the theoretical total energy in the Jahn–Teller distorted structure proposed by Kanamori. [Copyright &y& Elsevier]

Abstract: We performed the hybrid-density functional theory (DFT) calculations for the strongly correlated perovskite-type manganese fluorides of KMnF3, RbMnF3 and K1− x Li x MnF3 In both solids, UBHHLYP, which contains 50% Hartree–Fock exchange term, provided the reasonable effective exchange integral (Jab ) values, in comparison with the experimental ones. In order to investigate the intrinsic roles of counter cations precisely, we examined the variations of the total energy and Jab value, assuming the displacement of counter cation toward <100> direction. In KMnF3 (RbMnF3), it was found that the steric repulsion between potassium (rubidium) and bottleneck is large, while that between lithium and bottleneck is negligible in K1− x Li x MnF3. Finally, we also showed the possibility of the lithium ion conduction in the antiferromagnetic K1− x Li x MnF3. It was concluded that the lithium ion conduction in RMnF3 is possible, if the vacancy at R site exists. [Copyright &y& Elsevier]

Abstract: We performed hybrid-DFT calculations for La2/3− x Li3x TiO3 (LLT) with lithium ion conductivity, in order to investigate the detailed lithium ion conductive mechanism from the viewpoint of molecular orbital (MO) method. It was concluded that the very ionic lithium ion in bottleneck accelerates the lithium ion conduction. The calculated MO shows no chemical bonding between lithium ion and other ions. In comparison with the perovskite-type trivalent titanium oxide of LaTiO3, the effect of the titanium''s reduction was also investigated. We showed the possibility of the high lithium conductivity in LaTiO3. [Copyright &y& Elsevier]

When we estimate the proper bandgap for the perovskite-type titanium oxide of SrTiO3 by the use of hybrid-density functional theory (DFT) method, it is important to choose the exchange and correlation functionals. Especially, Hartree-Fock (HF) exchange functional plays the major role in inclusion of the localization effect. In this study, we empirically determined the proper HF exchange functional coefficient for SrTiO3. Though the blue-light emission process in SrTiO3 has attracted much interest, the mechanism is still unclear. To elucidate the mechanism of the blue-light emission process, we performed hybrid-DFT calculations for the oxygen deficient cluster models. It was concluded that oxygen deficiency is irrelevant to the process, because of the strong chemical bond between titaniums. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [ABSTRACT FROM AUTHOR]

When we estimate the proper bandgap for the perovskite-type titanium oxide of SrTiO3 by the use of hybrid-density functional theory (DFT) method, it is important to choose the exchange and correlation functionals. Especially, Hartree-Fock (HF) exchange functional plays the major role in inclusion of the localization effect. In this study, we empirically determined the proper HF exchange functional coefficient for SrTiO3. Though the blue-light emission process in SrTiO3 has attracted much interest, the mechanism is still unclear. To elucidate the mechanism of the blue-light emission process, we performed hybrid-DFT calculations for the oxygen deficient cluster models. It was concluded that oxygen deficiency is irrelevant to the process, because of the strong chemical bond between titaniums. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [ABSTRACT FROM AUTHOR]

Electronic states of copper oxides were investigated after hole-doping by using Hybrid-DFT (UB2LYP) calculations for three types of model clusters. Energy diagram in hole-doped state is explained by using d-p interaction between 3d x 2 -y 2 orbital of copper and 2p orbital of oxygen and superexchange interaction (SE) between copper orbitals via closed oxygen orbital. Copper oxides Hole-doping Density Functional Theory (DFT) CASSCF Superexchange (SE) interaction Superconductivity [ABSTRACT FROM AUTHOR]

The unrestricted Hartree-Fock (UHF) and hybrid density functional theory (HDFT) calculations have been carried out for manganese oxides. In order to elucidate magnetic properties of the species, the effective exchange integrals ( J ab ) have been obtained by the total energy difference between the highest and lowest spin states. The natural orbital analysis has also been performed for elucidation of symmetry and occupation numbers of the magnetic orbitals. [ABSTRACT FROM AUTHOR]