Takeshi Mukoyama

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.

The electronic structure of rare-earth oxides in the creation of the core hole

Abstract We studied the electronic structures of rare-earth sesqui-oxides R 2 O 3 (R: rare-earth element) with a core hole, both experimentally and theoretically. The experimental study was made by measuring the rare-earth 3d X-ray photoemission spectra (XPS) of these oxides. Clear double-peak structures were observed for La 2 O 3 , the shoulder or broad foot of the low-binding-energy side of 3d XPS were observed for Pr 2 O 3 , Nd 2 O 3 , and Sm 2 O 3 , and single-peak structures were observed for Eu 2 O 3 , Gd 2 O 3 , and Dy 2 O 3 . The calculation of electronic structures was performed for the ground state and the 3d –1 core-hole states by the spin-unrestricted DV-Xα molecular-orbital method for model clusters chosen as [RO 6 ] 9– for R 2 O 3 . The calculated results show the difference of the electronic structure in the ground state and the core-hole states. In the creation of the core hole, the number of unpaired 4f electrons increases by less than one due to the weak charge-transfer effect for La 2 O 3 and Ce 2 O 3 , and this corresponds to the clear double-peak structure of the rare-earth 3d XPS. For Eu 2 O 3 and Yb 2 O 3 , the number increases and decreases by less than 1 due to the restricted charge-transfer effect by filling 4f↑ and 4f orbitals with electrons. Due to the strong charge-transfer effect, the number of unpaired 4f electrons increase by more than 1 for Pr–Sm oxides, and this effect produces, the shoulder or broad foot in the low-binding-energy side of the rare-earth 3d XPS peak. The decrease by more than 1 for Gd–Tm oxides results in clear single peak structures. The present results indicate that rare-earth sesqui-oxides can be classified into the four groups by spin response.

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 ...

Fitting of Gaussian to peaks by non-iterative method

Abstract A method for fitting a Gaussian spectrum without iterative procedure is presented. The method utilizes a linearization technique of the Gaussian function and the standard linear least-squares fitting. Experimental and pseudo-experimental peaks have been used to test this method and a comparison with the conventional non-linear least-squares method has been made. The present method has the advantages of not requiring the initial estimates of Gaussian parameters, and not requiring large computer memory.

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.

Systematic study of helium-induced L shell ionization cross sections

Abstract An experimental data set consisting of about 500 published cross section values has been applied to test the performance of various theoretical approximations for the description of the helium-induced L-subshell ionization of heavy elements (Z2 = 66−92). The large discrepancy observed previously between the L2-subshell data and the predictions of the ECPSSR model has been greatly reduced including the effect of the collision-induced intrashell transitions. Further improvements in the description of the data, particularly for the L3 Subshell, have been achieved modifying the binding energy correction of the ECPSSR theory according to the recent suggestion by Vigilante et al. The use of more realistic electronic wave functions than those applied in ECPSSR is discussed as a possible way to remove the remaining discrepancies.

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.

Electronic structures of 3d transition metal (Ti–Cu) oxides probed by a core hole

Abstract Electronic structures of various 3d transition metal oxides are calculated using the spin-unrestricted discrete-variational (DV) Hartree–Fock–Slater (Xα) method for the ground state and 1s −1 core hole state. Model clusters MO n are used in place of calculating infinite size solids, where M is the transition metal elements from Ti ( Z =22) to Cu ( Z =29) and n the coordination number of oxygen; n =6 for O h symmetry and n =4 for T d or D 4h symmetry. The calculated results indicate that the number of unpaired 3d electrons reduces in the creation of the core hole for late transition metal compounds, i.e. do not represent the ground-state spin state for these compounds, but conserves for early transition metal compounds. These results provide theoretical basis on the validity of spin selective X-ray absorption spectroscopy for early transition metal compounds by using the high-resolution X-ray fluorescence yield method, and theoretical basis on the validity or nonvalidity of spin state analysis using core-level spectroscopy, such as X-ray emission, X-ray absorption, and photoelectron spectroscopies. It is also found that the spin of a class of compounds sometimes flips in the creation of the core hole.

Range of electrons and positrons

Abstract The range of electrons and positrons in detector materials has been calculated by the Wilson theory. The results obtained are compared with the values estimated from the continuous-slowing-down model. A correction factor which depends only on the energy is presented. It is concluded that the corrected Wilson theory yields good approximate values for ranges of electrons and positrons in the energy region above 70 keV.

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.