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  • Articles  (990)
  • Atomic, Molecular and Optical Physics  (990)
  • Wiley-Blackwell  (990)
  • American Meteorological Society
  • 1
    Electronic Resource
    Electronic Resource
    Parallel computational chemistry made easier: The development of NWChem (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 56 (1995), S. 475-483 
    Details
    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 describe the design philosophy, structure, and supporting tool kits of the NWChem computational chemistry package. The primary purpose of this effort was to develop efficient parallel algorithms for a broad range of methods commonly used in computational chemistry. To facilitate this, we developed a shared nonuniform access memory model which simplifies parallel programming while at the same time providing for portability across both distributed- and shared-memory machines. In addition to this specific focus on parallelization, a substantial effort has been made to simplify the general problem of large-scale software development, which is common to many research groups. We find that this simplification can be achieved through judicious use of ideas from the computer science field of software engineering in the design and implementation of the program with minimal extra effort on the part of the chemist. © 1995 John Wiley & Sons, Inc.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560560851
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  • 2
    Electronic Resource
    Electronic Resource
    Ladder operators for central potential wave functions from the algebraic representation of orthogonal polynomials (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 155-164 
    Details
    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: A general algebraic procedure that yields to raising and lowering operators for the solutions of second-order differential equations is presented. The method is illustrated by applying it to the differential equations of Hermite and Laguerre polynomials. Taking advantage of the algebraic representation of these polynomials, the ladder operators for harmonic oscillator and hydrogen atom wavefunctions are straightforwardly deduced without resorting to specialized factorizations. The proposed algebraic approach can be extended to the determination of new sets of ladder operators that could be used in the calculation of matrix elements in specific applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400818
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  • 3
    Electronic Resource
    Electronic Resource
    An Ab Initio computational scheme for polymeric chains with fully converged coulomb and exchange lattice sums (1991)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 40 (1991), S. 603-618 
    Details
    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 restricted Hartree-Fock formalism applied to quasi one-dimensional translational systems embodies slowly convergent Coulomb and exchange lattice summations. In this contribution, an algorithm based on a Filon like quadrature procedure to carry out the k-space integration of density matrix elements is analyzed and its efficiency is illustrated by its application to the linear chains of hydrogen molecules. It allows the computation of Coulomb and exchange lattice sums to their asymptotic limit, and renders obsolete the empirical procedure of guessing the number of interactions to be included in the calculations.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560400854
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  • 4
    Electronic Resource
    Electronic Resource
    Alternative approach to the factorization method (1992)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 44 (1992), S. 171-179 
    Details
    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: A procedure to obtain the operational solutions of second order differential equations related with Sturm-Liouville problems is presented. The method is based on the commutation relation between the ladder operators themselves, with a certain structure, and the position and momentum operators. Even though the creation and annihilation operators, derived by the proposed approach, factorize as expected the corresponding differential equation, the method does not use, as original premise factoring, the differential relation under consideration. That is, the displayed procedure is quite different, simple, and direct when compared with other procedures such as the factorization method of Infeld and Hull. To illustrate the above, the usefulness of the proposed procedure is shown by finding the ladder operators associated to the quantum numbers n and I for various potential wave functions. © 1992 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560440816
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  • 5
    Electronic Resource
    Electronic Resource
    Improved recursion formulas for the calculation of two-center central potential integrals (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 56 (1995), S. 339-347 
    Details
    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: A commutator algebra procedure is used to get improved recurrence relations for the calculation of any f(r) off-diagonal two-center matrix elements in the general case of displaced arbitrary central potential wave functions. As expected, the proposed formulas reduce properly to the generalized recursion equations for the calculation of one-center integrals. Besides, when f(r) = rk, one obtains the equivalent of the Kramer rule for two-center multipolar matrix elements for arbitrary potentials, and when f(r) is constant, the Wu formula (for the calculation of Franck-Condon factors) is ameliorated in the sense that the new relation not necessarily considers equal mass. Furthermore, all diagonal matrix elements as well as all off-diagonal integrals between nondisplaced potentials appear, in our treatment, as particular cases in good agreement with already published results. As a useful application, the corresponding recurrence relations for the calculation of one-center hydrogenic matrix elements and two-center Kratzer potential integrals are given as examples. However, our approach is general and can be easily extended to obtain recursion formulae for other potential wave functions. © 1995 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560560838
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  • 6
    Electronic Resource
    Electronic Resource
    Potentials of an alternative scheme for ab initio polymer band structure calculations. Illustration on the chain of hydrogen atoms (1989)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 36 (1989), S. 341-351 
    Details
    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 alternative scheme for ab initio polymer band structure calculations based on a Filon-type quadrature is proposed. This scheme avoids the explicit calculation and the storage of the “troublesome” Fourier transforms of the LCAO density matrix elements and is a first step towards a better control of the convergence of the different lattice sums appearing in the configuration space LCAO-SCF-CO method. The potential of the proposed technique is illustrated by a minimal basis set calculations on an infinite chain of H atoms.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560360317
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  • 7
    Electronic Resource
    Electronic Resource
    Dependence of RHF properties of hydrogen and helium chains on the exchange lattice summations (1990)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 593-606 
    Details
    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 alternative configuration space scheme for ab initio polymer band structure calculations based on a Filon-type quadrature is proposed. This scheme avoids the explicit calculation and the storage of the “troublesome” Fourier transforms of the LCAO density matrix elements. Furthermore, the lattice sums (Coulomb and exchange) can be carried out up to infinity which removes the difficult problem of guessing limits to these summations. The potential of the proposed technique is illustrated by minimal basis set calculations on the infinite chains of H and He atoms.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560382458
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  • 8
    Electronic Resource
    Electronic Resource
    Theoretical study of [Li(H2O)n]+ and [K(H2O)n]+ (n = 1-4) complexes (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 53 (1995), S. 49-56 
    Details
    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 geometries, successive binding energies, vibrational frequencies, and infrared intensities are calculated for the [Li(H2O)n]+ and [K(H2O)n]+ (n = 1-4) complexes. The basis sets used are 6-31G* and LANL1DZ (Los Alamos ECP+DZ) at the SCF and MP2 levels. There is an agreement for calculated structures and frequencies between the MP2/6-31G* and MP2/LANL1DZ basis sets, which indicates that the latter can be used for calculations of water complexes with heavier ions. Our results are in a reasonable agreement with available experimental data and facilitate experimental study of these complexes. © 1995 John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560530108
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  • 9
    Electronic Resource
    Electronic Resource
    Information entropies of many-electron systems (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 56 (1995), S. 489-498 
    Details
    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 Boltzmann-Shannon (BS) information entropy Sρ = ∫ ρ(r)log ρ(r)dr measures the spread or extent of the one-electron density ρ(r), which is the basic variable of the density function theory of the many electron systems. This quantity cannot be analytically computed, not even for simple quantum mechanical systems such as, e.g., the harmonic oscillator (HO) and the hydrogen atom (HA) in arbitrary excited states. Here, we first review (i) the present knowledge and open problems in the analytical determination of the BS entropies for the HO and HA systems in both position and momentum spaces and (ii) the known rigorous lower and upper bounds to the position and momentum BS entropies of many-electron systems in terms of the radial expectation values in the corresponding space. Then, we find general inequalities which relate the BS entropies and various density functionals. Particular cases of these results are rigorous relationships of the BS entropies and some relevant density functionals (e.g., the Thomas-Fermi kinetic energy, the Dirac-Slater exchange energy, the average electron density) for finite many-electron systems. © 1995 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560560507
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  • 10
    Electronic Resource
    Electronic Resource
    Vibrational frequencies of sodium clustersWork presented at “Thirty Years of Density Functional Theory: Concepts and Applications,” Cracow, Poland, June 13-16, 1994. (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 56 (1995), S. 589-601 
    Details
    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 vibrational frequencies of NaN clusters (2 ≤ N ≤ 72) are calculated by direct diagonalization of the dynamical matrix. Density functional theory with a spherically averaged pseudopotential is used to compute the total energy. The geometry is optimized by the simulated annealing technique. Contributions to the Hessian matrix due to electron relaxation following the ionic displacements are calculated in linear response theory. The frequencies are in the range 0-220 cm-1 and the electron relaxation strongly modifies those of the modes dominated by radial oscillations, particularly the breathing mode frequencies that are proportional to N-1/3. The filling of atomic shells produces a stepwise behavior of the highest frequencies. The giant dipole resonance energies are obtained as a byproduct of the calculation. © 1995 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560560515
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