Library

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Atomic, Molecular and Optical Physics  (9)
Material
Keywords
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 19 (1981), S. 207-216 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The coupled-cluster approach to obtaining the bond-state wave functions of many-electron systems is extended, with a set of physically reasonable approximations, to admit a multiconfiguration reference state. This extension permits electronic structure calculations to be performed on correlated closed- or open-shell systems with potentially uniform precision for all molecular geometries. Explicit coupled cluster working equations are derived using a multiconfiguration reference state for the case in which the so-called cluster operator is approximated by its one- and two-particle components. The evaluation of the requisite matrix elements is facilitated by use of the unitary group generators which have recently received wide attention and use in the quantum chemistry community.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 2
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 16 (1979), S. 1209-1237 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Le formalisme des fonctions de Green de polarisation dans la notation utilisant les superopérateurs de Goscinski et Lukman a été réétabli avec un état de référence MC-SCF pour obtenir le métrique des superopérateurs. Les avantages potentiels de cet état de référence plus général ainsi que certains points faibles inhérents associés aux états de référence utilisés traditionnellement dans les théories de perturbation Hartree-Fock ou Rayleigh-Schrödinger sont discutés brièvement. L'hermiticité des superopérateurs est analysée dans le cadre des états de référence MC-SCF. Utilisant une notion d'ordre propre à cet état de référence on présente des formules explicites et des procédés de calcul pour la réalisation de cette théorie des fonctions de Green, qui sont spécialisés pour inclure des termes consistants jusqu'au second ordre.
    Abstract: Der Formalismus für Green'sche Funktionen von Polarisierungstyp in der Superoperatorbezeichnung von Goscinski und Lukman wird mittels eines MC-SCF-Referenzzustands hergeleitet. Die möglichen Vorteile mit diesem allgemeineren Referenzzustand und gewisse mit den in den traditionellen Hartree-Fock- oder Rayleigh-Schrödinger-Störungstheorien verwendeten Referenzzuständen verbundene eigene Schwächen werden kurz diskutiert. Die Hermitizität der Superoperatoren wird im Rahmen des MC-SCF-Referenzzustands analysiert. Mittels eines für diesen Referenzzustand geeigneten Ordnungsbegriffs werden explizite Formeln und Rechnungsverfahren für die Implementierung dieser Theorie von Green'schen Funktionen vorgelegt und spezialisiert um Glieder bis zur zweiten Ordnung einzuschliessen.
    Notes: The polarization Green's-function formalism in the superoperator notation of Goscinski and Lukman is re-derived using a multiconfiguration self-consistent-field (MC-SCF) reference state to establish the superoperator metric. The potential advantages of employing this more general reference state in Green's-function theories and certain inherent weaknesses associated with the traditional Hartree-Fock or Rayleigh-Schrödinger perturbation theory reference state choices are briefly discussed. The Hermiticity of the superoperators is analyzed within the framework of the MC-SCF reference state. Using a concept of order appropriate for this reference state choice, explicit formulas and computational procedures for the implementation of this Green's-function theory are presented and specialized to include terms consistent through second order.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 31 (1987), S. 3-16 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Based upon the invariance of N-particle systems under discrete operations of reflection, inversion, and rotation by 2π/n, a method for obtaining complete sets of relations among energy derivatives of all orders has been presented. The method is based on the criterion that, for a discrete symmetry operation such as reflection across a plane; the change in energy due to simultaneous arbitrary displacements of each particle is equal to another set of “conjugate” displacements of all particles. Applications of the above relations for particular molecular systems possessing a combination of symmetry operations is also presented. Here, via the row echelon analysis, the number of independent derivatives are found, and simple symmetry relations that allow determination of the remaining derivatives are presented. For example, for a homonuclear diatomic molecule with D2h symmetry only 1 of the 6 first derivatives and 1 of the 21 second derivatives need to be independently calculated.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 33 (1988), S. 27-40 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Given the invariance of an N-body system under discrete operations of reflection, inversion, a rotation by 2π/n, and the corresponding relations among the derivatives of energy, we have constructed through an invertible transformation a set of active and redundant coordinates. Movement along the active coordinates preserves all symmetry relations. We show that algorithms for locating stationary points or for calculating reaction paths are exactly separable in these active and redundant coordinates. We further show that this formalism is equally applicable when equations of constraints among coordinates are specified for the movement of particles. This includes geometrical constraints on bond lengths, angles, substituent group internal rotations, etc. This formalism enhances the efficiency since (laborious) cartesian derivatives need to be calculated only for the active variables and that the problem is reduced in term of m(≤3N) variables. We apply this procedure to obtain the equilibrium geometry of H2O molecule within the subspace of C2v symmetry configurations ab initio derivatives.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 311-323 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Determining mechanisms of chemical reactions involves finding dynamical paths between desired (given) reactant and product states. We have developed a method that is based on recasting the principle of stationary action into a general and computationally tractable form that yields all dynamical paths connecting the initial and final configurations of the system. Thus the method has advantages over the traditional initial-value trajectory calculations for solving such boundary value problems. We give some examples of reaction paths for H(2S) + O2(3Σg-) ↔ OH(2II) + O(3P) on the ground state potential energy surfaces HO2(2A″).
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 39 (1991), S. 747-754 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An orthogonalization procedure is presented that allows construction of at least (n-m) vectors orthogonal to {Xj}, j equals; 1, m, by linear combinations solely among {ηi}, i equals; 1, n, n〉m, and 〈Xj/ηi〉≠0. An important application of the procedure is in effective core potential methods for which valence orbitals can be constructed that are orthogonal to the core orbitals and yet involve no component of the core. Thus, a separate calculation for only the valence electrons can be performed without any explicit reference to the core electrons (orbitals).
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 43 (1992), S. 855-871 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two aspects of the problems of calculating steepest descent paths and locating stationary points on surfaces E(X), which are sources of some confusion in the literature, are addressed. These include writing proper expressions for the gradient and Hessian, and their transformation properties relative to coordinate transformations, based on the invariance of the surface E(X). The appropriate transformation is derived, based on a constrained energy minimization condition, to achieve what we call the Hessian eigenvalue representation. This not only allows decoupling of the variables, but also points to the minimization direction and preserves the eigenvalues of the Hessian. These results allow one to use the steepest descent path and stationary point location algorithms in any coordinate system and obtain invariant results. The validity of these considerations are also confirmed through numerical examples. The stationary condition with constrained kinematic path length is also shown to yield a Hessian eigenvalue representation for the normal modes for small vibrations. Lastly, we have constructed a mathematically consistent definition of mass-weighted Cartesians where the intrinsic reaction path of Fukui is a steepest descent path. © 1992 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 163-173 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have used the ab initio technique of UHF/LANL 1 MB to study the interactions between absorbed oxygen atoms and molecules with their host nickel lattice. The host lattice is approximated by a small cluster of nickel atoms that are arranged as face-centered-cubic, except for a tubular void described by the absence of three or four lattice elements. The oxygen absorbates are placed, one at time, within this cavity. We conclude that, for tubular cavities, the interaction between the nickel lattice and the oxygen absorbates is stronger than the interactions between pairs of oxygen atoms, suggesting that the absorbates are mostly atomic (as apposed to diatomic) in character, while the (energetically) most preferred number of oxygen atoms to reside inside an n-site, tubular hollow of nickel is simply (n - 1). © 1993 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 759-767 
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Calculations have been performed on low-lying states of SF6 and SF6- at the complete active space multiconfiguration self-consistent field (CAS-MCSCF) level. These calculations involved optimization of basis function exponents, particularly the f-functions on sulfur and their effect on the potential energies and the SF6 electron affinity. The CAS-MCSCF calculations for the anion and neutral included 4,863 and 2,115 configuration functions, respectively. Octahedral and selected distorted geometries were considered. The ground-state equilibrium geometries correspond to the octahedral configuration of SF6 (1A1g), R(S—F) = 1.56 Å, ωe = 776 cm-1, and of the anion SF6-(2A1g), R(S—F) = 1.70 Å, ωe = 558 cm-1. The adiabatic and vertical electron affinities are found to be -0.63 and 1.8 eV, respectively. Electron autodetachment phenomena associated with the anion are also discussed and a possible mechanism for this process is presented. © 1993 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...