Showing papers by "Yasuyuki Ishikawa published in 2007"
TL;DR: Complementary calculations confirm the assignment of the ground state of the UO(2) molecule as a (3)Phi(2u) state that arises from the 5f(1)7s( 1) configuration.
Abstract: The ground and excited states of the UO2 molecule have been studied using a Dirac-Coulomb intermediate Hamiltonian Fock-space coupled cluster approach (DC-IHFSCC). This method is unique in describing dynamic and nondynamic correlation energies at relatively low computational cost. Spin-orbit coupling effects have been fully included by utilizing the four-component Dirac-Coulomb Hamiltonian from the outset. Complementary calculations on the ionized systems UO2+ and UO22+ as well as on the ions U4+ and U5+ were performed to assess the accuracy of this method. The latter calculations improve upon previously published theoretical work. Our calculations confirm the assignment of the ground state of the UO2 molecule as a Φ2u3 state that arises from the 5f17s1 configuration. The first state from the 5f2 configuration is found above 10000cm−1, whereas the first state from the 5f16d1 configuration is found at 5047cm−1.
90 citations
TL;DR: In this article, a combined direct molecular dynamics/density-functional theoretical study of the electrooxidation of hydrogen at the Pt(1/1)/water interface has been carried out to provide insights into the reaction mechanism.
73 citations
TL;DR: In this article, the transition energies of the superheavy element lawrencium, including the ionization potential, excitation energies and electron affinities, were calculated by the intermediate Hamiltonian coupled cluster method.
Abstract: Transition energies of the superheavy element lawrencium, including the ionization potential, excitation energies and electron affinities, are calculated by the intermediate Hamiltonian coupled cluster method. A large basis set (37s31p26d21f16g11h6i) is used, as well as an extensive P space (6s5p4d2f1g). The outer 43 electrons are correlated. Accuracy is monitored by applying the same approach to lutetium, the lighter homologue of Lr, and comparing with experimentally known energies. QED corrections are
included. The main goal is to predict excitation energies, in anticipation of planned spectroscopy of Lr.
The ground state of Lr is $7s^27p\ ^2{\rm P}_{1/2}$
, unlike the $5d6s^2\ ^2{\rm D}_{3/2}$
of Lu. Predicted Lr excitations with large transition moments in the prime range for the planned experiment, 20 000–30 000 cm-1, are 7p→8s at 20 100 cm-1
and 7p→7d at 28 100 cm-1. The average absolute
error of 20 excitation energies of Lu is 423 cm -1, and the error limits for Lr are put at 700 cm-1.
The two electron affinities measured recently for Lu are reproduced within 55 cm-1, and a third bound state of Lu- is predicted.
44 citations
TL;DR: In this article, the ionization potential and excitation energies of atomic nobelium (element 102) are calculated in preparation for a planned experiment, using a large basis set, which correspond to all excitations from correlated occupied orbitals to virtual orbitals in a large space.
Abstract: The electronic spectrum of atomic nobelium (element 102) is calculated in preparation for a planned experiment. The intermediate-Hamiltonian (IH) coupled-cluster method is applied to the ionization potential and excitation energies of the atom, using a large basis set $(37s\phantom{\rule{0.2em}{0ex}}31p\phantom{\rule{0.2em}{0ex}}26d\phantom{\rule{0.2em}{0ex}}21f\phantom{\rule{0.2em}{0ex}}16g\phantom{\rule{0.2em}{0ex}}11h\phantom{\rule{0.2em}{0ex}}6i)$ and correlating the outer 42 electrons. All the levels studied are obtained simultaneously by diagonalizing the IH matrix. The rows and columns of this matrix correspond to all excitations from correlated occupied orbitals to virtual orbitals in a large $P$ space $(8s\phantom{\rule{0.2em}{0ex}}6p\phantom{\rule{0.2em}{0ex}}6d\phantom{\rule{0.2em}{0ex}}4f\phantom{\rule{0.2em}{0ex}}2g\phantom{\rule{0.2em}{0ex}}1h)$, and the matrix elements are ``dressed'' by including excitations to the higher virtual orbitals ($Q$ space) at the coupled cluster singles-and-doubles level. Lamb shift corrections are included. The accuracy is assessed by applying the same method to ytterbium, the lighter homologue of No. The calculated ionization potential of Yb is within $3\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$ of experiment, and the average error in the lowest 20 excitation energies of the atom is $300\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. Nobelium is the heaviest element for which a reliable semiempirical estimate of the ionization potential exists, $6.65(7)\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$; the calculated value of $6.632\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ is in excellent agreement. Transition amplitudes are obtained from an extensive relativistic configuration interaction calculation. The outstanding feature of the predicted nobelium spectrum is a very strong line at $30\phantom{\rule{0.2em}{0ex}}060\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, with an amplitude $A=5.0\ifmmode\times\else\texttimes\fi{}{10}^{8}\phantom{\rule{0.3em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, corresponding to the $7s7p$ $^{1}P_{1}\ensuremath{\rightarrow}7{s}^{2}$ $^{1}S_{0}$ transition. Putting the error limit conservatively at $0.1\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, we predict a strong feature in the No spectrum at $30\phantom{\rule{0.2em}{0ex}}100\ifmmode\pm\else\textpm\fi{}800\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$.
37 citations
TL;DR: The electronic properties of double strands composed of trimeric LNA, PNA, DNA and RNA single strands were investigated by density-functional molecular orbital calculations and results are comparable to the experimental finding that PNA and LNA single strands display high affinity toward a complementary DNA or RNA single strand.
35 citations
TL;DR: In this article, a re-investigation of n=3, Δn=0 transitions in the EUV spectra of Na-, Mg-, Al-like, and Si-like ions of Au was presented.
Abstract: Many-body perturbation theory (MBPT) calculations are an adequate tool for the description of the structure of highly charged multi-electron ions and for the analysis of their spectra. We demonstrate this by way of a re-investigation of n=3, Δn=0 transitions in the EUV spectra of Na-, Mg-, Al-like, and Si-like ions of Au that have been obtained previously by heavy-ion accelerator based beam-foil spectroscopy. We discuss the evidence and propose several revisions on the basis of our multi-reference many-body perturbation theory calculations of Ne- through P-like ions of Au.
25 citations
TL;DR: In this article, a number of different H-atom abstraction paths were observed, with four isomeric (CH 4 N 2 ) products being formed: CH 3 N NH, CH 3 NHN, H 2 C NNH 2, and CH 2 NHNHNH.
Abstract: Reactive collisions between CH 3 NNH 2 + NO 2 and CH 3 NHNH + NO 2 were observed via direct molecular dynamics simulations. The simulations, which are classical trajectories whose dynamics were dictated by forces derived from quantum mechanics-based calculations, were conducted: (1) to confirm the importance of reaction paths expected to play a role in the ignition and combustion of monomethylhydrazine/nitrogen tetroxide (MMH/NTO) and monomethylhydrazine/red fuming nitric acid (MMH/RFNA) systems, and (2) for their potential to identify unexpected mechanisms. A number of different H-atom abstraction paths were observed, with four isomeric (CH 4 N 2 ) products being formed: CH 3 N NH, CH 3 NHN, H 2 C NNH 2 , and CH 2 NHNH. All abstractions were barrierless, including those from the methyl group. Reaction exothermicities, which were characterized via QCISD/6-311+G(d,p)//MPWB1K/6-31+G(d,p) calculations, ranged from 2 to 36 kcal/mol. The results suggest that finite rate chemical kinetics mechanisms for MMH/NTO and MMH/RFNA systems should include steps for the production and decomposition of CH 3 NHNH, H 2 C NNH 2 , CH 2 NHNH, and CH 3 NHN in addition to those for CH 3 NNH 2 and CH 3 N NH.
21 citations
TL;DR: A combined molecular dynamics/density-functional theoretical study was carried out to address the propensity of ambient water to form cross-strand bridging water (CSBW) and their effects on the electronic properties of a fully hydrated DNA duplex 5'-d(CCATTAATGG)(2)-3'.
20 citations
TL;DR: In this article, a new implementation of double-group symmetry to relativistic Gaussian spinors is presented for four-component molecular calculations, in which the authors show that the systematic adaptability to irreducible representations under arbitrary pointgroup symmetry, as well as Kramers symmetry, is inherent in the present basis spinors, which possess the analytic structure of Dirac atomic spinors.
Abstract: A new, practical implementation of double-group symmetry to relativistic Gaussian spinors is presented for four-component relativistic molecular calculations. We show that the systematic adaptability to irreducible representations under arbitrary point-group symmetry, as well as Kramers (time-reversal) symmetry, is inherent in the present basis spinors, which possess the analytic structure of Dirac atomic spinors. The implementation of double-group symmetry entails significant computational efficiencies in the relativistic second-order Moller–Plesset perturbation calculation on Au2 and the density functional theory (DFT) calculation with the B3LYP functional on octahedral UF6, in which the highest symmetries used are, respectively, C and D. The four-component B3LYP equilibrium geometry of UF6 is reported. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
19 citations
TL;DR: Simulations based on classical molecular dynamics and semiempirical molecular orbital methods obtained the current-voltage characteristics for single- and double-strand DNAs that are qualitatively in agreement with the experimental results.
17 citations
01 Mar 2007
TL;DR: In this article, the authors discuss some n = 3, Δn = 0 transitions in the EUV spectra of Na-, Mg-and Al-like ions of Au that have been observed by electron beam ion trap work and by heavy-ion accelerator based beam-foil spectroscopy.
Abstract: Spectroscopic measurements on few-electron high-Z ions take guidance from isoelectronic trends of low-Z to mid-Z ions and from theory. Such wide-range extrapolations, however, are fraught with uncertainty. We discuss as examples some n = 3, Δn = 0 transitions in the EUV spectra of Na-, Mg- and Al-like ions of Au that have been observed by electron beam ion trap work and by heavy-ion accelerator based beam-foil spectroscopy. New insights are gained from notable recent progress of calculations.
TL;DR: The electronic properties of double-stranded octametric DNA-DNA and LNA-DNA with a single-base mismatch were compared with those having fully complementary base pairs to quantify the effect of the base mismatch on hybridization energies (HE).
TL;DR: In this article, a relativistic R-matrix close-coupling method is developed and implemented based on effective many-body Hamiltonians for accurate representation of the target and collisional states in multielectron ions.
Abstract: A relativistic R-matrix close-coupling method is developed and implemented based on effective many-body Hamiltonians for accurate representation of the target and collisional states in multielectron ions The effective Hamiltonian in relativistic multireference many-body perturbation theory accurately accounts for short-range many-body interactions unaccounted for in the extant nonrelativistic and Breit-Pauli R-matrix methods The method is successfully applied to the near-threshold electron impact excitation of the 3s{sup 2} {sup 1}S{yields}3s3p {sup 3}P transition in Mg-like argon (Ar{sup 6+}) ion where the observed disagreement between the experimental absolute total cross sections and those predicted by using the Breit-Pauli R-matrix method reveals an inadequacy of the R-matrix methods based on the configuration-interaction representation of the basis states
27 Mar 2007
TL;DR: In this paper, a multireference M{o}ller-Plesset perturbation theory has been employed to calculate with high accuracy the energy levels and transition probabilities of Cu-to-S-like gold ions.
Abstract: Relativistic multireference M{o}ller-Plesset perturbation theory has been employed to calculate with high accuracy the energy levels and transition probabilities of Cu- to Sr-like gold ions. The many-body calculations were carried out to identify the unassigned blended lines in the 35-40 angstroms region of the low-energy EBIT spectrum of the gold ions. Most of the prominent lines in the 35-40 angstroms region were identified as the emission lines in Sr-like gold.