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Lin Y.-C.,Center for Theoretical and Computational Chemistry | Sundholm D.,University of Helsinki
Journal of Physical Chemistry A | Year: 2012

The molecular structures of low-lying isomers of anionic and neutral sodium auride clusters have been studied computationally at the second-order Møller-Plesset perturbation theory level using quadruple-Χ basis sets augmented with a double set of polarization functions. The first vertical detachment energies were calculated at the Møller-Plesset level as the energy difference between the cluster anion and the corresponding neutral cluster. The photodetachment energies of higher-lying ionization channels were calculated by adding electronic excitation energies of the neutral clusters to the first vertical detachment energy. The excitation energies were calculated at the linear response approximate coupled-cluster singles and doubles level using the anionic cluster structures. The obtained ionization energies for NaAu -, NaAu 2-, NaAu 3-, NaAu 4-Na 2Au 2-, Na 2Au 3-, Na3Au 3-, and Na 2Au 4- were compared to values deduced from experimental photoelectron spectra. Comparison of the calculated photoelectron spectra for a few energetically low-lying isomers shows that the energetically lowest cluster structures obtained in the calculations do not always correspond to the clusters produced experimentally. Spin-component-scaled second-order Møller-Plesset perturbation theory calculations shift the order of the isomers such that the observed clusters more often correspond to the energetically lowest structure, whereas the spin-component-scaled approach does not improve the photodetachment energies of the sodium aurides. The potential energy surface of the sodium aurides is very soft, with several low-lying isomers requiring an accurate electron correlation treatment. The calculations show that merely the energetic criterion is not a reliable means to identify the structures of the observed sodium auride clusters; other experimental information is needed to ensure a correct assignment of the cluster structures. The cluster structures of nonstoichiometric anionic sodium aurides have been determined by comparing calculated ionization energies for low-lying structures of the anionic clusters with experimental data. © 2012 American Chemical Society.

Kvaal S.,University of Oslo | Kvaal S.,Center for Theoretical and Computational Chemistry
Journal of Chemical Physics | Year: 2012

The curse of dimensionality (COD) limits the current state-of-the-art ab initio propagation methods for non-relativistic quantum mechanics to relatively few particles. For stationary structure calculations, the coupled-cluster (CC) method overcomes the COD in the sense that the method scales polynomially with the number of particles while still being size-consistent and extensive. We generalize the CC method to the time domain while allowing the single-particle functions to vary in an adaptive fashion as well, thereby creating a highly flexible, polynomially scaling approximation to the time-dependent Schrödinger equation. The method inherits size-consistency and extensivity from the CC method. The method is dubbed orbital-adaptive time-dependent coupled-cluster, and is a hierarchy of approximations to the now standard multi-configurational time-dependent Hartree method for fermions. A numerical experiment is also given. © 2012 American Institute of Physics.

Samdal S.,Center for Theoretical and Computational Chemistry | Guillemin J.-C.,National Graduate School of Chemistry, Rennes | Gundersen S.,University of Oslo
Journal of Physical Chemistry A | Year: 2010

The molecular structure of trichloroethenylgermane, CH2 - CH-GeCl3, has been determined by electron diffraction and supported by quantum chemical calculations on CH2 - CH-MX3 (M = C, Si, Ge, Sn and X = H, Cl). An equilibrium syn conformation with Cs symmetry is obtained both experimentally and theoretically where one of the Ge-Cl bonds eclipses the C - C bond. The barrier of internal rotation about the C-Ge bond is determined to be V3 = 5.3(7) kJ mol-1 using a dynamic model to simulate the internal motion. The most important structure parameters (estimated re/Å and ∠/degree) are: r(C-Ge) = 1.911(5), r(C - C) = 1.345(5), r(Ge-Cl7) = 2.122(2),

Onishi T.,Mie University | Onishi T.,Center for Theoretical and Computational Chemistry
International Journal of Quantum Chemistry | Year: 2010

Many research activities on the solid-state oxide fuel cell (SOFC) have been performed for production of electronic energy without fossil fuel. To design the efficient SOFC electrolyte, we should clarify the detailed mechanism on oxide ion conduction. LaAlO3 perovskite has been much expected as the electrolyte material. It is known that strontium doping at lanthanum site lowers the activation energy for the oxide ion conduction. In this study, we have investigated the mechanism of the activation energy decrease in strontium-doped LaAlO3 by the cluster model calculations based on hybrid density functional theory. It was concluded that the ionic and covalent bonds between counter cation and conductive oxide ion is responsible for the activation energy change. © 2010 Wiley Periodicals, Inc.

Zeng Z.H.,Center for Theoretical and Computational Chemistry | Zeng Z.H.,CAS Dalian Institute of Chemical Physics | Ma X.F.,Center for Theoretical and Computational Chemistry | Ma X.F.,CAS Dalian Institute of Chemical Physics | And 4 more authors.
Science China Chemistry | Year: 2010

Combined with third generation synchrotron radiation light sources, X-ray photoelectron spectroscopy (XPS) with higher energy resolution, brilliance, enhanced surface sensitivity and photoemission cross section in real time found extensive applications in solid-gas interface chemistry. This paper reports the calculation of the core-level binding energy shifts (CLS) using the first-principles density functional theory. The interplay between the CLS calculations and XPS measurements to uncover the structures, adsorption sites and chemical reactions in complex surface chemical processes are highlight. Its application on clean low index (111) and vicinal transition metal surfaces, molecular adsorption in terms of sites and configuration, and reaction kinetics are domonstrated. © Science China Press and Springer-Verlag Berlin Heidelberg 2010.

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