Search

Previously, we have performed the spin-polarized hybrid-density functional theory (HUDFT) calculations for elucidating magnetic properties of the two-dimensional (2D) K2NiF4 and K2CuF4 solids. In Part I, it has been concluded that the half-and-half-(HH-) type HUDFT method is one of the best calculation methods for these species. On the other hand, in Part II, we have demonstrated that potential curves for cluster models of K2CuF4 and KCuF3 are reasonably calculated by the HH-type HUDFT method under the approximate spin projection, and the lattice distortion resulted by Jahn-Teller effect is expressed as the second-order polynomial. In this study, we pay attention to the three-dimensional (3D) magnetic interactions in KNiF3. Our effective exchange integral Jab schemes for 3D cluster models such as KNi8F12 (4) with and without point charges have provided the reasonable Jab values (-30.24–34.48 cm-1), in comparison with the experimental one (-30.58 cm-1). The 3D magnetic interactions have been investigated from viewpoints of the Mulliken spin density and charge density populations, the natural orbital analysis, and chemical indices. Point charges located in positions of fluorine anion adjacent to cluster model have reproduced Jab values well. Roles of potassium as counter cation in KNiF3 solid were also investigated. It was concluded that potassium has a role of stabilizing the 3D magnetic structures. Finally, the mutual relationships between broken-symmetry and symmetry-adapted approaches are discussed on the basis of chemical indices. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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]

Helium Covalency Chemical bonding rule Dimer Cubic structure In order to investigate the helium covalency, molecular orbital calculations were performed for helium dimer and helium-containing La2/3-xLi3xTiO3 perovskite and HeC8 cube. There were orbital overlap between helium 1s orbitals in helium dimer. In HeTi8O12 and HeC8 models, helium had orbital overlap with oxygen and carbon, respectively. From chemical bonding rule, it was concluded that helium can form covalent bonding with oxygen and carbon. [ABSTRACT FROM AUTHOR]

At room temperature, cubic SrTiO3perovskite exhibits only paraelectric property, although ferroeletric properties appear in tetragonal BaTiO3and PbTiO3. In this study, the new high-performance ferroelectric such as SrTiO2C perovskite was theoretically designed. Cluster model calculations based on hybrid density functional theory were performed to clarify a ferroelectric mechanism of SrTiO2C. It has been concluded that SrTiO2C can be utilised for a ferroelectric material of a high-speed memory, due to the extremely small polarisation-inversion energy. [ABSTRACT FROM PUBLISHER]

Hybrid Kohn-Sham calculations are performed to clarify the proton-conduction mechanism in Sc-doped SrTiO3 perovskite, from the viewpoint of energetics and bonding. The calculated potential energy curves are discussed and a molecular-orbital analysis performed. Much hydrogen can exist around doped scandium, where it is energetically stabilized. However, scandium-doping has no energetic advantage in the activation energy for proton-conduction. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

We theoretically designed the new sodium ion-conductors such as NaAlO(CN)2 and NaxAl1-x/3(CN)3 perovskite. From the viewpoint of the energetics and bonding, the sodium ion-conductive mechanism was investigated for LaAlO3, NaAlO(CN)2, and NaxAl1-x/3(CN)3 perovskite. It was concluded that NaAlO(CN)2 perovskite can be utilized as a sodium ion-conductor for sodium-sulfur battery. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Hybrid-DFT calculations were performed to clarify the hydrogen transport mechanism in SrTiO3 perovskite. From a molecular-orbital analysis, we discussed the changes of the chemical bonding between conductive hydrogen and others, and the proton conduction paths. It is concluded that the conductive hydrogen is almost neutral, with a diagonal conduction path favored inside of Ti4O4 square. We considered the nitrogen doping at the oxygen site to enhance the proton conductivity. Doped nitrogen exists as the part of NH2− ion, enhancing proton conductivity. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012 [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]

Previously, we demonstrated that the lithium ion conduction in the perovskite-type manganese fluoride is attributed to counter cation-site vacancy mechanism. The divalent counter cation-doped KxBa(1-x)/2MnF3 was theoretically predicted as the lithium ion conductor in the perovskite-type manganese fluoride. In this study, we considered the oxygen doping for KxBa(1-x)/2MnF3 to realize the higher lithium ion conductivity. It is because lithium ion forms the stronger ionic bond with the doped oxygen anion. The hybrid-DFT calculations were performed to investigate the lithium ion conduction in the oxygen-doped KxBa(1-x)/2MnF3. The calculation results were discussed from the viewpoints of the potential energy curve, electron densities, and charge and spin densities. The effect of the lithium ion fluctuation was also discussed by calculating the ratio of the diffusion coefficients. Finally, we theoretically predicted the ideal oxygen-doped structure for KxBa(1-x)/2MnF3. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [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]

In the perovskite-type titanium oxides, the changes of magnetic properties by GdFeO3-type lattice distortion are observed. In this study, we have performed cluster model calculations based on the density functional theory method, and have obtained the effective exchange integral (Jab) in order to elucidate the magnetic change by the GdFeO3-type lattice distortion. The components of deciding the orbital ordering and magnetic property have also been discussed. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [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]

We propose a process for easily fabricating a unique one-dimensional fullerene crystal, i.e., a fullerene finned-micropillar (FFMP). To fabricate a one-dimensional fullerene crystal more easily than when using current processes, fullerene was first annealed at 1173 K for 1 h with an argon gas flow of 0.5 L/min. We then examined how the FFMP structure changed when the fabrication process conditions, such as temperature, annealing time, and argon gas flow rate, were varied. FFMPs can be prepared within a short time and may have the same electrical characteristics as other one-dimensional crystals, e.g., fullerene nanowhiskers, so they are expected to be very useful for field-effect transistors, organic photovoltaics, and so on in the near future. [ABSTRACT FROM AUTHOR]