Hirohide Nakamatsu

Four-component relativistic density functional calculations of heavy diatomic molecules

We perform accurate four-component calculations for heavy closed-shell diatomic molecules in the framework of relativistic density functional theory using local and gradient corrected density functional schemes. As examples we have chosen Cu2, Ag2, Au2, Tl2, Pb2, Bi2, and Pt2. The potential energy curves show the quality, and the discrepancies of the density functionals unscreened from any approximation of the relativistic effects.

Theoretical x‐ray absorption spectra of SF6 and H2S

We have performed molecular orbital calculations for SF6 and H2S, using the discrete–variational Xα method. Energies and cross sections of virtual states are obtained for theoretical spectra of sulfur K, LII,III and fluorine K x‐ray absorptions for the SF6 molecule. They are in good agreement with the experimental results. Through the same calculation procedures, the theoretical spectra of sulfur K and LII,III absorptions for H2S are derived. The obtained molecular orbitals represent the experimental spectra below the ionization energy very well. SF6 has distinct shape resonances above the ionization energy, in contrast to H2S which has pre‐edge peaks as a main structure. For the SF6 molecule, shape resonances come from the scattering at the steep change of attractive potential of surrounding fluorine atoms. It is demonstrated that phase shift due to the scattering causes the resonances without a potential barrier. Various spectral differences among the sulfur K, LII,III and the fluorine K absorptions in ...

Relativistic effects on the electronic structure and chemical bonding of UF6

We have studied the relativistic effects in the electronic structure and chemical bonding for the ground state of UF6, using the relativistic and nonrelativistic discrete‐variational Xα molecular orbital calculations. It is found that two relativistic effects appear in the valence levels; the energy level splitting and upward shift of energies of the molecular orbitals. From the Mulliken population analysis of the valence levels, it is shown that the level splitting is due to mixing of the uranium atomic orbitals with a strong spin–orbit interaction, such as U6p, and the upward shift due to the increase in the screening of the nuclear charge and charge redistribution. The strength of U–F bonding remarkably increases for the relativistic case, because the changes in the radial distributions due to the relativistic effects induce both the decrease in the antibonding interactions and the increase in the bonding ones.

Electron-microscopic observation of photodeposited Pt on TiO2 particles in relation to photocatalytic activity

We have shown that the shape and dispersion of photodeposited Pt on TiO2 particles are drastically changed by varying the sacrificial organic reagents present in aqueous solution. The Pt deposits were in good contact with TiO2 and showed oriented growth. Although the Pt deposits were distributed at random even around the steps at the surface without pretreatment, preillumination treatment caused preferential deposition on some terraces around the steps at the TiO2 surface. Induced lattice defects were observed by transmission electron microscopy near the TiO2 surface following photocatalytic reaction. The photocatalytic activity is closely related to the degree of Pt dispersion. The factor determining the degree of Pt dispersion is discussed, and a new model for photodeposition in solution is proposed.

DV-Xα calculation on resonances in X-ray absorption spectra of SF6

Abstract We have performed molecular orbital calculations for SF 6 , using the discrete-variational Xα method. The theoretical energies for the resonances near the X-ray absorption edges for the sulfur atom are in good agreement with the experimental results. The resonances correspond to the wavefunctions which have very large amplitude at the sulfur atom. The present results indicate that the resonances originate from the interference between the wavefunctions in the central sulfur atom those scattered by the surrounding fluorine atoms. Other types of resonances are also found and their wavefunctions are spread over the molecule.

DV-Xα Molecular Orbital Method for X-ray Absorption Near Edge Structure–Application to N2 and CrO42-

We have performed DV-Xα molecular orbital calculations for XANES of the N2 and CrO42- species to confirm our conclusions concerning the origin of shape resonances reported before. The theoretical spectra in the present work are in good agreement with the experimental spectra. Shape resonances for the N2 molecule are examined and, as well as the previous works, found to-be due to electron scattering by the attractive potential of molecule, neither due to centrifugal barrier nor another potential barrier.

Discrete-variational Dirac-Slater calculation on XPS for the valence levels of UF6

Abstract Relativistic molecular orbital calculations of the valence electronic structure of UF 6 were done using the discrete-variational Dirac-Slater method (DV-DS). Theoretical ionization energies of the UF 6 valence levels were evaluated by means of Slaters transition-state method. The ionization energies and relative X-ray photoelectron spectrum intensities of UF 6 valence levels calculated in the present work are in good agreement with the experimental X-ray photoelectron spectrum.

IONIC AND COVALENT BONDS IN CEO2 CRYSTAL

Abstract We have performed cluster calculations in a study of the bonding nature in the CeO 2 crystal using the relativistic discrete-variational Xα method. The electron charge distribution of CeO 2 is compared with those of ZrO 2 and CaF 2 . The charge density in the metal atomic region indicates stronger covalency for CeO 2 than that in Zr for ZrO 2 . The repulsion between the metal and oxygen ionic cores is, however, strong and superior to the covalent interaction, and thus the ionic character determines the static bonding nature in the CeO 2 crystal. A population analysis shows that the mixed interaction due to the independent ionic and covalent contributions arises from the ionic Ce 5s, 5p and covalent Ce 4f, 5d orbitals which are proximate to each other in the bond region.

Relation between X-ray absorption near-edge spectra and interatomic distances

Abstract We have performed first-principles calculations for the X-ray absorption near-edge structure (XANES) of PX 3 (X = F, Cl) molecules and AO 4 n − (A = P, S, Cl) cluster ions, using the discrete Xα method. Theoretical X-ray spectra for PX 3 agree with the experimental ones. The theoretical spectra for AO 4 n − correspond to the major peaks in the experimental spectra which have been identified as contributions of the AO 4 n − clusters in the M n AO 4 (M = Li, Na, K, Rb, Cs) compounds. In the theoretical as well as the experimental spectra, the peak energies vary with the P-X and A-O interatomic distances. The XANES spectra and the wavefunctions are examined in terms of potential scattering. The results indicate that the wavefunction in each intra-atomic region is essential to approximate the whole quasi-standing wave of a shape resonance. In consistency with the calculated results, a model of the wavefunction is proposed for the XANES peaks of simple molecules and an equation is derived which expresses a relation among interatomic distance, peak energy and atomic number. The interatomic distances calculated with this equation including three optimized parameters have a notably high correlation with the experimental data for the free molecules involving B, C, N, O and F atoms.

Theoretical study on the UV excited states of UF6 using the discrete-variational Dirac—Slater calculation method

Abstract We have performed the relativistic molecular orbital calculations for the ground and UV excited states of UF 6 , using the discrete-variational Dirac—Slater method. For the ground state of UF 6 , the formation of the UF bonding is explained by the relativistic MOs, in contrast to the non-relativistic MOs which fail to give the bonding character between the U and F atoms. The theoretical excitation energies for the charge transfer transitions are in good agreement with the experimental UV absorption spectrum. The changes in the bond overlap population of the excitation can explain the experiments that the excitation in the A—X band leads to fluorescence, while that in the B—X band to the dissociation of UF bonding. This suggests that the difference in the character of the de-excitation processes is mainly determined by the bonding nature for the initial and the final levels on the excitation.