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  • 1
    Electronic Resource
    Electronic Resource
    Quantum Monte Carlo: Direct calculation of corrections to trial wave functions and their energies (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 9699-9702 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report an improved Monte Carlo method for calculating the difference δ between a true wave function Ψ and an analytic trial wave function Ψ0. The method also produces a correction to the expectation value of the energy for the trial function. The nodes of the trial function are not corrected and the energy is corrected to the fixed-node energy of the trial function. Applications to several sample problems as well as to the water molecule are described. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481606
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  • 2
    Electronic Resource
    Electronic Resource
    Improved estimates of the total correlation energy in the ground state of the water molecule (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 7706-7708 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two new calculations of the electronic energy of the ground state of the water molecule yield energies lower than those of any previously reported variational calculations. A fixed-node quantum Monte Carlo calculation gives −76.420(1) hartrees and an analytic variational calculation gives −76.4274 hartrees. These values lie only 17 and 11 mhartrees, respectively, above the "experimental" value.© 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473770
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  • 3
    Electronic Resource
    Electronic Resource
    The interaction potential of a symmetric helium trimer (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 8999-9001 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The interaction potential of three helium atoms in symmetric linear configurations is calculated under the Born–Oppenheimer approximation using an "exact'' Green's function quantum Monte Carlo method. The results are compared with those of "exact'' quantum Monte Carlo calculations for the helium dimer and the Axilrod–Teller triple-dipole energy expression. For nearest neighbor separations of 5.6 bohrs, the equilibrium distance for a helium dimer, the corresponding trimer energy is −21.5±1.9 K, compared to −22.3±0.2 K, calculated for pairwise additive behavior. For all internuclear separations in the neighborhood of the van der Waals well (∼5.6 bohrs), the nonadditive contribution is found to be very small.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467258
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  • 4
    Electronic Resource
    Electronic Resource
    First-row hydrides: Dissociation and ground state energies using quantum Monte Carlo (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 7573-7578 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Accurate ground state energies comparable to or better than the best previous ab initio results can be obtained using the fixed-node quantum Monte Carlo (FN-DQMC) method. The residual energy, the nodal error due to the error in the nodal structure of a trial wave function, is examined in this study using nodal surfaces given by near HF-limit wave functions. The study is aimed at better understanding of the nodal error and the cancellation of nodal errors in calculating energy differences. Calculations have been carried out for the first-row hydrides LiH to FH and the corresponding atoms. The FN-DQMC ground state energies are among the lowest to date. The dissociation energies De have been calculated with accuracies of 0.5 kcal mol−1 or better. For all hydrides, the dissociation energies are consistent with experimental values. The fixed-node quantum Monte Carlo method can therefore offer a very straight-forward way to calculate highly accurate dissociation energies. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472584
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  • 5
    Electronic Resource
    Electronic Resource
    Accurate quantum Monte Carlo calculations for hydrogen fluoride and the fluorine atom (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 4636-4640 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quantum Monte Carlo calculations of the ground state energies of the fluorine atom and the hydrogen fluoride molecule have been carried out using both fixed-node and released-node methods. The fixed-node total energies for both F and FH are among the most accurate available. The fixed-node dissociation energy De=141.3(4) kcal mol−1 is in excellent agreement with experimental data. The cancellation of the nodal error was achieved with trial wave functions having nodal surfaces determined by Slater determinants of the near Hartree–Fock limit quality. With the released-node Green's function quantum Monte Carlo method the lowest upper bounds to the ground state energies to date for both F [E0=−99.731(4) Hartree] and FH [E0=−100.458(5) Hartree] have been obtained. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472306
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  • 6
    Electronic Resource
    Electronic Resource
    Simplified sampling in quantum Monte Carlo: Application to H+3 (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2839-2843 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new procedure for sampling molecular wave functions in quantum Monte Carlo calculations is used to determine energies for a number of configurations of the molecular ion H+3. With the Green's function fixed by use of a trial energy and with no drift terms required for importance sampling the procedure is both simple and efficient. For the equilibrium configuration of H+3 the energy is found to be −1.343 76±0.000 03 a.u. (i.e., ±0.02 kcal/mol).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452034
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  • 7
    Electronic Resource
    Electronic Resource
    Quantum chemistry by random walk: A faster algorithm (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 2662-2663 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two extensions of the fixed-node random walk method of solving the Schrödinger equation are described. A simple iterative procedure is found to reduce time-step error and the use of two trial wave functions in place of one for importance sampling is found to reduce computation effort. In combination the two modifications reduce computation effort for a fixed accuracy by a factor of about 10.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448262
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  • 8
    Electronic Resource
    Electronic Resource
    An exact quantum Monte Carlo calculation of the helium–helium intermolecular potential. II (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 4546-4548 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report "exact" ab initio calculations with reduced statistical error for the potential energy of interaction of two helium atoms. For the equilibrium internuclear distance of 5.6 bohr, the calculated electronic energy is −5.807 483 53±0.000 000 06 hartrees and the corresponding well depth is (ε/k) 10.98±0.02 K. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1390512
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  • 9
    Electronic Resource
    Electronic Resource
    Quantum chemistry by random walk: Application to the potential energy surface for F+H2→HF+H (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 7237-7239 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452326
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  • 10
    Electronic Resource
    Electronic Resource
    Direct Monte Carlo simulation of chemical reaction systems: Internal energy transfer and an energy-dependent unimolecular reaction (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 6607-6612 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a direct Monte Carlo simulation of an energy-dependent unimolecular reaction system of the type A→B in which the rates of the reactions of specific states Ai of A increase with their internal energies. Intermolecular exchange of translational and internal energies among colliding species Ai+Aj→Ak+Al is incorporated with use of a simple flexible statistical model satisfying all requirements of momentum and energy conservation, microscopic reversibility, and equilibrium. The required calculations are straight forward and rapid. The observed variation of overall reaction rate with pressure deviates from that of a simple Lindemann–Christiansen mechanism. For unrestricted energy exchange allowing transitions between all levels of A the deviations are small. For restricted (ladder) energy exchange limited to transitions up or down one level per collision the deviations are larger and the behavior is similar to that observed in a number of experimental studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466185
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