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  • 1
    Title: Monte Carlo methods in ab initio quantum chemistry; 1
    Author: Hammond, B. L.
    Contributer: Lester, W. A. , Reynolds, P. J.
    Publisher: Singapore u.a. :World Scientific,
    Year of publication: 1994
    Pages: 304 S.
    Series Statement: World Scientific lecture and course notes in chemistry 1
    Type of Medium: Book
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  • 2
    Title: Recent advances in quantum Monte Carlo methods /; 2,2
    Contributer: Lester, W. A. , Rothstein, Stuart M. , Tanaka, Shigenori
    Publisher: Singapore :World Scientific,
    Year of publication: 2002
    Pages: XII, 315 S. : , ill
    Series Statement: Recent advances in computational chemistry 2,2
    Type of Medium: Book
    Language: English
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 1905-1906 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It is demonstrated that the short-time Green's function often used in diffusion quantum Monte Carlo simulations of the Schrödinger equation generates an unbiased probability distribution in the limit of vanishing time step τ. For finite τ, an error is introduced into the potential which is of O(τ). An expression for this term is derived.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2639-2652 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Polyatomic indirect photodissociation is treated as a quantum transition between quasidiscrete and dissociative (photofragment) states. Our adiabatic method is followed to describe the nuclear dynamics of the dissociative state. Ab initio MCHF excited electronic potential energy surfaces are constructed and used to determine heavy-particle dynamics. The theory is applied to single-photon predissociation of C2N2(C˜ 1Πu) at 164, 158.7, and 153.6 nm to form CN(X 2Σ+)+CN(A 2Π). Theoretical predictions are found to be in good agreement with recent experimental product vibrational energy distributions.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4867-4870 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio Hartree–Fock calculations were performed on FeAr and FeAr+ in order to determine the interaction of both neutral and singly-ionized Fe atoms trapped in Ar, and on ArFeCO and FeCOAr in order to ascertain the effect of an Ar matrix on the FeCO molecule. Quadrupole splittings and isomer shifts are computed using ab initio orbital populations and charge densities scaled by a relativistic factor. Good agreement between calculated and experimental hyperfine parameters is found in each case. The interaction energy for Fe+–Ar has been computed by ab initio Hartree–Fock and effective-core potential (ECP) methods. Both approaches yield a minimum between Fe+ and Ar at approximately 7.6 bohr.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 4749-4750 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quantum Monte Carlo (QMC) is used to compute the electronic energies of H2(B 1Σ+u) and H2(E 1Σ+g). The E state calculation represents the first application of QMC to a molecular excited state with the same symmetry as a lower state. In this QMC approach a trial function specifies the nodes of the QMC distribution. The role of these nodes in excited state calculations is discussed. QMC energies that contain over 95% of the correlation energy are computed using MCSCF wave functions as trial functions.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 552-561 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using a new Monte Carlo method for computing properties of excited quantum states, correlation function quantum Monte Carlo, we calculate the lowest ten vibrational excited state energies of H2O and H2CO in the Born–Oppenheimer approximation. The statistical errors for H2O are 0.1 cm−1 for the ground state and 15 cm−1 for the tenth excited state while for H2CO they are 2 cm−1 for the ground state and 30 cm−1 for the eighth excited state. The algorithm presented here is easily extensible to larger systems.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 2013-2021 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Recent quantum Monte Carlo (QMC) studies of electronic structure have considered various trial function enhancements directed at improved fixed-node energies. In this study we investigate complete active space self-consistent field (CASSCF) trial functions in the diffusion Monte Carlo (DMC) method. We study longer CASSCF expansions than typically used in QMC studies and optimize correlation function parameters, basis function coefficients, and configuration state function mixing coefficients. To perform a stable, efficient wavefunction optimization, sample points are analytically obtained from an integrable probability density function or a Monte Carlo walk guided by a positive definite function. The approach is applied to acetylene and its dissociation fragments (C, CH, C2, C2H, C2H2). For these systems 70%–90% of the correlation energy is recovered with variational MC and 91%–98% with DMC. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 9028-9032 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The relative energies, binding energies, and adsorption energies of three CuSi4 and two CuSi6 clusters have been computed in the fixed-node diffusion Monte Carlo (FNDMC), CASSCF, and B3LYP DFT methods. These results are compared with the earlier Hartree–Fock (HF) and B3LYP DFT investigations of these systems by two of us [C. Xiao and F. Hagelberg, J. Mol. Struct.: THEOCHEM 529, 241 (2000)]. The very close energy level spacing of the isomers under consideration confirms the previous work of Xiao and Hagelberg. The FNDMC results show some qualitative discrepancies with B3LYP DFT, and HF findings. They also confirm the appropriateness of the B3LYP DFT method for the prediction of the most stable CuSi4 isomer, while the CASSCF method compares more favorably with FNDMC for adsorption energies than B3LYP DFT. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 2680-2683 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The quantum Monte Carlo (QMC) method is used to compute the atomization energy and the heat of formation of the propargyl radical, C3H3. The effective core potential and fixed-node approximations are used in the diffusion Monte Carlo (DMC) variant of QMC. Two generalized gradient approximation density functionals, B3LYP and B3PW91, are also applied for comparison. The atomization energy determined by these methods is 606.12 kcal/mol (B3LYP), 610.24 kcal/mol (B3PW91), and 607.6(0.6) (DMC). The latter compares favorably with separate measurements of 608.0(3.0) and 608.5(1.2) kcal/mol. The ΔHf298 determined by these methods is 84.03 kcal/mol (B3LYP), 79.91 kcal/mol (B3PW91), 82.5(0.6) (DMC), and two independent measurements yield values of 82.5(3.0) and 81.5(1.2) kcal/mol. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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