Showing papers by "Yasuyuki Ishikawa published in 1996"

Calculated energy levels of thallium and eka-thallium (element 113).

Abstract: Multiconfiguration Dirac-Fock and relativistic coupled cluster results are reported for electron affinities, ionization potentials, and excitation energies of Tl and element 113 and their cations. Large basis sets are used, with l up to 6, the Dirac-Fock or Dirac-Fock-Breit orbitals found, and the external 35 electrons of each atom are correlated by the coupled-cluster method with single and double excitations. Very good agreement with experiment is obtained for the Tl transition energies. As in the case of elements 111 [Eliav et al., Phys. Rev. Lett. 73, 3203 (1994)] and 112 [Eliav, Kaldor, and Ishikawa, Phys. Rev. A 52, 2765 (1995)], strong relativistic stabilization of the 7s orbital is observed for E113, leading to dramatic reduction (relative to Tl) in the energies of excitation from ${\mathit{d}}^{10}$ to ${\mathit{d}}^{9}$ levels. Thus the ${\mathit{d}}^{10}$s\ensuremath{\rightarrow}${\mathit{d}}^{9}$${\mathit{s}}^{2}$ energy of ${\mathrm{E}113}^{2+}$ is 0.1 eV, compared to 8 eV for ${\mathrm{Tl}}^{2+}$. It is predicted that divalent or trivalent compounds of E113 with an open 6${\mathit{d}}^{9}$ shell could possibly exist. The calculated electron affinities of Tl and E113 are 0.40\ifmmode\pm\else\textpm\fi{}0.05 and 0.6\char21{}0.7 eV, respectively. \textcopyright{} 1996 The American Physical Society.

Element 118: The First Rare Gas with an Electron Affinity.

Abstract: The electron affinity of the rare gas element 118 is calculated by the relativistic coupled cluster method based on the Dirac-Coulomb-Breit Hamiltonian. A large basis set (34{ital s}26{ital p}20{ital d}14{ital f}9{ital g}6{ital h}4{ital i}) of Gaussian-type orbitals is used. The external 40 electrons are correlated. Inclusion of both relativity and correlation yields an electron affinity of 0.056eV, with an estimated error of 0.01eV. Nonrelativistic or uncorrelated calculations give no electron affinity for the atom. {copyright} {ital 1996 The American Physical Society.}

Transition energies of barium and radium by the relativistic coupled-cluster method

Abstract: The relativistic coupled-cluster method is used to calculate ionization potentials and excitation energies of the barium and radium atoms and their monocations. Large basis sets are used, with {ital l} up to 5, the Dirac-Fock or Dirac-Fock-Breit orbitals found, and the external 28 electrons of barium or 42 electrons of radium are correlated by the coupled-cluster method with single and double excitations. Good agreement (within a few hundred wave numbers) is obtained for the ionization potentials and low excitation energies (up to 3 eV for Ba, 4 eV for Ra). The Breit interaction has little effect on the excitation energies, but it improves significantly the fine-structure splittings of Ra. Large relativistic effects on the energies are observed, up to 1 eV for barium and 2 eV for radium. The nonrelativistic ground states of Ba{sup +} and Ra{sup +} are ({ital n}{minus}1){ital d} {sup 2}{ital D} rather than {ital ns} {sup 2}{ital S}. {copyright} {ital 1996 The American Physical Society.}

Conformational potential energy surface of the FSO radical and its isomer FOS in the ground 2A″ state

Abstract: The structure and spectroscopic properties of the ground 2 A″ state FSO radical and its isomer, FOS, are determined at the single and double excitation quadratic configuration interaction level of theory with a 6-311G(2df) Gaussian basis set. The local minimum corresponding to the isomer FOS lies about 84 kcal mol −1 above the global minimum structure corresponding to the FSO radical. A number of single-point QCISD calculations were performed with a smaller 6-311G ∗ basis set to obtain the qualitative features of the conformational potential energy surface for the isomerization FSO → FOS .