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  • 1995-1999  (5)
  • 1970-1974
  • 1965-1969
  • Theoretical, Physical and Computational Chemistry  (5)
  • 1
    Electronic Resource
    Electronic Resource
    Quantum dynamics with Lanczos subspace propagation: Application to a laser-driven molecular system (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 67 (1998), S. 273-285 
    Details
    ISSN: 0020-7608
    Keywords: Lanczos propagation ; laser-molecule interaction ; Chebyshev propagation ; time-dependent Schrödinger equation ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two Lanczos subspace propagation techniques are discussed in this work and compared with the Chebyshev method applied to the original Hamiltonian matrix. Both procedures involve the use of a reduced propagator in the Lanczos subspace to calculate the solution to the time-dependent Schrödinger equation but differ in the way the propagator is evaluated. The LSC (Lanczos subspace Chebyshev) expresses the propagator in terms of Chebyshev polynomials that are functions of the tridiagonal Hamiltonian matrix in the Lanczos space. In contrast, the LSV (Lanczos subspace variational) is implemented by solving the eigenproblem in the Lanczos subspace and then performing a variational expansion of the propagator in the M-dimensional eigenvector space. Although the LSV is the same as the reduced propagator scheme proposed by Park and Light, in the present study the LSV is implemented as a one-step long-time propagator. As a numerical example, the interaction of a molecule with a strong laser pulse is investigated. The Hamiltonian is explicitly time dependent in this case, and thus the stationary formalism is employed in this work to solve the time-dependent Schrödinger equation. Application of either the LSC or LSV yields a wave function in the M-dimensional Lanczos subspace. Nonetheless, the transition amplitudes computed from this wave function are in excellent agreement with those calculated by direct application of the Chebyshev method in the original space used to define the Hamiltonian matrix.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 67: 273-285, 1998
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Torsional eigenvalues of the water trimer on several ab initio potential surfaces (1998)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 68 (1998), S. 233-252 
    Details
    ISSN: 0020-7608
    Keywords: water trimer ; torsional eigenvalues ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Eigenvalues corresponding to the three torsional degrees of freedom were calculated for the water trimer and its deuterated isotopomer in four sets of calculations involving different potential energy surfaces. The four potential surfaces were developed in this work by reparametrization of the CKL function against four sets of ab initio energies calculated with and without counterpoise correction. Transition frequencies corresponding to the low-frequency torsional motions of the trimer were calculated and then compared with those found from experiment to assess the accuracy of each potential energy surface. Although reparametrization of the CKL function to a set of counterpoise-corrected energies yielded transition energies that are in qualitative agreement with those from experiment, reparametrization to another set of counterpoise-corrected energies resulted in highly inaccurate values of the transition energy. As a consequence, our results demonstrate that caution must be exercised in the implementation of the counterpoise method as it does not always lead to more accurate ab initio calculations.   © 1998 John Wiley & Sons, Inc. Int J Quant Chem 68: 233-252, 1998
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 3
    Electronic Resource
    Electronic Resource
    Efficient treatment of out-of-plane bend and improper torsion interactions in MM2, MM3, and MM4 molecular mechanics calculations (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 1804-1811 
    Details
    ISSN: 0192-8651
    Keywords: molecular mechanics ; geometric statement function method ; in-plane and out-of-plane bend ; improper torsion ; MM2, MM3, and MM4 force fields ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: Simple and very efficient formulas are presented for four-body out-of-plane bend (used in MM2 and MM3 force fields) and improper torsion (used in the MM4 force field) internal coordinates and their first and second derivatives. The use of a small set of bend and stretch intermediates allows for order of magnitude decreases in calculation time for potential energies and their first and second derivatives, which are required in molecular mechanics calculations. The formulas are eminently suitable for use in molecular simulations of systems with complicated bond networks.   © 1997 John Wiley & Sons, Inc.   J Comput Chem 18: 1804-1811, 1997
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
  • 4
    Electronic Resource
    Electronic Resource
    Finite difference Poisson-Boltzmann electrostatic calculations: Increased accuracy achieved by harmonic dielectric smoothing and charge antialiasing (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 268-276 
    Details
    ISSN: 0192-8651
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: A common problem in the calculation of electrostatic potentials with the Poisson-Boltzmann equation using finite difference methods is the effect of molecular position relative to the grid. Previously a uniform charging method was shown to reduce the grid dependence substantially over the point charge model used in commercially available codes. In this article we demonstrate that smoothing the charge and dielectric values on the grid can improve the grid independence, as measured by the spread of calculated values, by another order of magnitude. Calculations of Born ion solvation energies, small molecule solvation energies, the electrostatic field of superoxide dismutase, and protein-protein binding energies are used to demonstrate that this method yields the same results as the point charge model while reducing the positional errors by several orders of magnitude. © 1997 by John Wiley & Sons, Inc.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 5
    Electronic Resource
    Electronic Resource
    Treatment of multibody interactions in molecular simulations of systems with general bond networks (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 18 (1997), S. 1513-1522 
    Details
    ISSN: 0192-8651
    Keywords: general bond network ; molecular simulation ; geometric statement function ; internal coordinates ; polymer ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: One of the most formidable difficulties in the computer programming of molecular simulations is the sometimes complicated bookkeeping required for keeping track of internal coordinates and their derivatives. A completely general method for keeping track of stretch (two-body), bend (three-body), and torsion, wag, and other four-body interactions for ANY bond network is presented. Computer code using this method for calculating internal coordinates and their derivatives can be used for completely different types of bond networks, no matter how complex, with little or no modification. The method is designed to incorporate recent improved formulas for calculating internal coordinates and their derivatives to ensure the most optimal calculation sequence.   © 1997 John Wiley & Sons, Inc.   J Comput Chem 18: 1513-1522, 1997
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
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