Chikatoshi Satoko

Discrete Variational Xα Cluster Calculations. I. Application to Metal Clusters

Applications of the discrete variational (DV) Xα molecular orbital method based on the self-consistent Hartree-Fock-Slater model to metal clusters are presented. Numerical basis functions are utilized in the present calculations. Variations of orbital energies and populations with exchange scaling parameter α are investigated. It is proved that the self-consistent-charge (SCC) approximation to the SCF method gives accurate orbital energies. The numerical basis SCC-DV-Xα method is shown to be very efficient for studies of rather large metal clusters such as Ni 13 .

Discrete Variational Xα Cluster Calculations. II. Application to the Surface Electronic Structure of MgO

Discrete variational (DV) Xα cluster method is extended to ionic crystals with inclusion of the long-ranged Coulomb potential of the ions outside the cluster. As a typical example of partially ionic crystals, the surface and the bulk electronic structures of MgO crystal are calculated. The strong electric field, the reduction in the Madelung potential and the charge redistribution on the surface are found to be important factors for the formation of the surface state. Various features of the DV-Xα cluster method, such as the size and the shape dependence of the cluster, the effect of the exterior potential and so on are investigated.

Theory of electronic structure of oxide surfaces

Abstract Recent theoretical studies on the electronic structures of oxide surfaces by the DV-Xα cluster method are reviewed. The aim is to elucidate the major material and structural factors governing the surface electronic structure. Special attention is paid to the properties of the electronic states which are related to the surface chemical activities. To give a comprehensive picture of the electronic structure of oxide surfaces, topics are selected from several different types of oxides including MgO, MO (where M denotes 3D transition metals), TiO2, SrTiO3, ReO3, ZnO. Electronic structure of oxygen chemisorbed on metals, which is the initial step of the oxide formation, is also studied. The important role of the partially filled d band and the influence of the chemisorption geometry is clarified in detail. Oxygen vacancy and other surface imperfections introduce localized electronic states, often with the energy level deep in the gap. They form active centers in the surface chemical processes. The charge compensation mechanism and the related peculiar properties of the polar surfaces are discussed. The chemisorption of oxygen, proton and hydroxyl on the oxide surface is investigated and the mechanism of the acidic and basic sites are discussed.

Discrete Variational X α Cluster Calculations. III. Application to Transition Metal Complexes

The discrete variational cluster calculations for perovskite type compounds KMeF 3 (Me=Cr, Mn, Fe, Co, Ni and Cu) and manganese dihalides MnX 2 (X=F, Cl and Br) have been made using the spin-polarized X α scheme. The calculated values of 10 D q and the transferred hyperfine constants are in good agreement with experiment. The d level splitting by the spin polarization is in accordance with the estimation from experimental Racah parameters. The level structure of the cluster is greatly improved by taking into account the potential from ions outside of the cluster, and shows good agreement with valence state XPS spectrum. The calculated excitation energies from ligand p to empty d and to conduction band can explain very well the u.v. spectra for MnX 2 . The halogen 3 d and 4 d are found to be important in level structures both for valence and lower excited regions of MnCl 2 and MnBr 2 .

Optical Properties of Single-Crystal Anatase TiO2

Polarized Reflection spectra of single-crystal anatase TiO 2 were measured in a photon energy range from 2 to 25 eV using synchrotron orbital radiation. Dielectric constants and absorption spectra were obtained from reflection spectra by Kramers-Kronig transformations. To interpret the structures that were observed in the spectra, the electronic states of anatase were calculated by using a cluster model with a size of Ti 5 O 14 . The structures observed in the energy region from 3 to 12 eV can be identified primarily due to the transition from O(2 p ) orbitals to Ti(3 d ) ones. The polarization dependence of the spectra in the above energy region is also effectively exhibited by the calculations from this model. The vague structures in the higher energy region (>12 eV) which can be clearly distinguished in spectra from the low energy part are due to the transition from O(2 p ) orbitals to Ti(4 s , 4 p ) ones.

Theory of the Surface Electronic Structure and Defect States of Rutile by the DV-X α Cluster Calculation

The discrete-variational (DV)-X α calculations are applied to the surface clusters Ti 4 O 16,15 and the bulk cluster Ti 3 O 15,14 of rutile (TiO 2 ) with and without the oxygen vacancy. For the clusters with the defect, an occupied localized state is obtained, whose orbital is mainly composed of the d states of the nearest Ti ions. The defect state energy for the surface cluster agrees with that obtained by UPS and ELS experiments. The change in the state density at the valence band calculated for (Ti 3 O 15,14 ) 18- cluster explains satisfactorily the change in the UPS spectra on the Ar or electron bombardment of the ordered (110) surface.

Surface Electronic Structure of SrTiO3 Studied by the DV-Xα Cluster Method

The electronic structure of SrTiO 3 (100) surface is investigated by the DV-Xα cluster method. It is demonstrated by the first principle, calculations that the intrinsic deep surface states do not exist on this surface. On the other hand the possibility of the three types of shallow surface states is suggested; A) those derived from x z , y z like d orbitals of surface Ti, B) those coming from 3 z 2 - r 2 like d orbital admixed with 4 p z , 4 s orbitals of surface Ti, and C) those associated with the surface O 2 p orbitals. The energy and properties of the localized electronic states induced by surface and bulk oxygen vacancies are calculated and compared with recent UPS and ELS experiments.

UV REFLECTION SPECTRA OF ANATASE TIO2

Abstract The polarized reflection spectra of anatase TiO 2 single crystals are measured in the photon energy range from 2 to 30 eV using the synchrotron orbital radiation in ISSP. The optical absorption coefficient is obtained from the reflection spectra by Kramers-Kronig analysis. Electronic states of anatase are calculated using a TiO 6 cluster model which symmetry is D 2d . The optical spectra are interpreted in terms of the calculated electronic states. The spectra in the energy range from 3 to 15eV are due to the transitions from O(2p) states to Ti(3d,4s) ones.

Surface Electronic Structure of TiO2 by the DV-Xα Cluster Calculation

The discrete variational Xα calculation is applied to various clusters of rutile to study the electronic structure of the bulk and (110) surface. The numerical result for the cluster including the removed oxygen site by the argon bombardment reveals the appearance of the defect state slightly below the conduction band, which corresponds with the observations by the UPS and ELS experiment.

LCAO-Xα-Force Study on Stable Structures of Si6 and Si10 Clusters

Stable structures of the Si 6 and the Si 10 microclusters have been calculated using LCAO-Xα-force method. The calculated structures of the Si 6 and the Si 10 clusters resemble a regular octahedron and a tetrahedron, respectively. In both clusters, triangles constituted of the (111)-surface atoms of the crystalline silicon contract by 20% in length compared to those of the crystal. This contraction is attributed to the interaction between dangling bonds and important for silicon microclusters of any size.