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  • 1
    Electronic Resource
    Electronic Resource
    Response to "Comment on ‘Quantum Monte Carlo study of the dipole moment of CO' " [J. Chem. Phys. 112, 4419 (2000)] (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 4421-4422 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In our previous publication we have mistakenly claimed that the applicability of the Hellmann–Feynman theorem in fixed-node quantum Monte Carlo calculations is not subject to the manner how the nodal boundary depends on an external parameter. This statement is not correct in general, except where the Hellmann–Feynman force is calculated for a nodal boundary which coincides with that of the unconstrained exact eigenfunction. We point out the error in our arguments and present an explicit expression for the correction term which supplements the Hellmann–Feynman force. This term can be interpreted as the linear response of the energy with respect to variations of the nodal region. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480997
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  • 2
    Electronic Resource
    Electronic Resource
    Quantum Monte Carlo study of the dipole moment of CO (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 11700-11707 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have calculated the dipole moment of CO along the potential energy curve using the pure diffusion quantum Monte Carlo method. Good agreement with coupled cluster singles–doubles calculations has been obtained throughout. An accurate treatment at the equilibrium distance requires a multi-reference trial wave function for which we obtained a dipole moment in accordance with experiment. We discuss the Hellmann–Feynman theorem within the fixed-node approximation in the case of field-dependent smoothly varying nodes. It is shown that the Hellmann–Feynman theorem is applicable to this case due to vanishing boundary contributions. A comparison has been made between the finite field correlated sampling approach and a direct calculation of the expectation value for the dipole moment operator. In the present application both methods perform equally well. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479170
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  • 3
    Electronic Resource
    Electronic Resource
    Quantum Monte Carlo study of Be2 and group 12 dimers M2 (M = Zn, Cd, Hg) (1998)
    Springer
    Theoretical chemistry accounts 99 (1998), S. 231-240 
    Details
    ISSN: 1432-2234
    Keywords: Key words: Quantum Monte Carlo ; Relativistic pseudopotentials ; Static dipole polarizabilities ; van␣der␣Waals molecules ; Fixed-node approximation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. Pure diffusion quantum Monte Carlo calculations have been carried out for Be2 and the weakly bound group 12 dimers Zn2, Cd2 and Hg2. We have applied relativistic energy-consistent large-core pseudopotentials and corresponding core-polarization potentials for the group 12 atoms. The derived spectroscopic constants (Re,␣De, ωe for Zn2 and Cd2 (Zn2: 3.88 ± 0.05 , 0.024 ± 0.007 eV, 25±2 cm−1; Cd2: 4.05 ± 0.03 , 0.031 ± 0.005 eV, 21±1 cm−1) are in good agreement with corresponding coupled-cluster results (Zn2: 4.11 , 0.022 eV, 21 cm−1; Cd2: 4.23 , 0.029 eV, 18 cm−1) and available experimental data (Zn2: 0.034 eV, 26 cm−1; Cd2: 0.039 eV, 23 cm−1). A comparison with previous results for the heavier homologue Hg2 is made. Using a multi-reference trial wavefunction for Be2 we achieved a sufficiently accurate description of the nodes of the wavefunction to obtain a bonding interaction within the␣fixed-node approximation. The applicability of this approach has been justified in pseudopotential and all-electron calculations. Covalent bonding contributions which appear in addition to pure van der Waals interactions for these molecules are analysed in terms of local occupation number operators and the associated interatomic charge fluctuations. Static dipole polarizabilities for group 12 atoms and dimers are calculated using a differential quantum Monte Carlo method for finite external electric fields. We have extended this method to pseudopotential calculations by taking into account the electric field dependence of the localized pseudopotentials. Within the statistical uncertainties our results agree with those from coupled-cluster calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002140050331
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  • 4
    Electronic Resource
    Electronic Resource
    On the bonding of small group 12 clusters (1999)
    Springer
    The European physical journal 6 (1999), S. 243-254 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 36.40.-c Atomic and molecular clusters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Characteristic properties as well as possible differences in bonding of small group 12 clusters ( , Cd, Hg; ) have been investigated by quantum chemical ab initio methods, i.e., relativistic large-core pseudopotentials, core-polarization potentials and coupled-cluster correlation treatments. A comparison of cohesive energies and spectroscopic properties like ionization potentials, electron affinities, and vibrational frequencies reveals a close similarity between the clusters of Cd and Hg. For Zn clusters we observed an exceptional increase in stability between and . In order to get a more qualitative picture of the covalent contributions to bonding we have calculated the electron localization function (ELF). The ELF analysis is in accordance with the calculated spectroscopic properties and shows predominant van der Waals interactions with weak covalent contributions for all the cluster sizes considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100500050341
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    Paper (German National Licenses)
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