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  • 1
    Electronic Resource
    Electronic Resource
    Nonlocal pseudopotentials and diffusion Monte Carlo (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 3467-3475 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have applied the technique of evaluating a nonlocal pseudopotential with a trial function to give an approximate, local many-body pseudopotential which was used in a valence-only diffusion Monte Carlo (DMC) calculation. The pair and triple correlation terms in the trial function have been carefully optimized to minimize the effect of the locality approximation. We discuss the accuracy and computational demands of the nonlocal pseudopotential evaluation for the DMC method. Calculations of Si, Sc, and Cu ionic and atomic states and the Si2 dimer are reported. In most cases ∼90% of the correlation energy was recovered at the variational level and excellent estimations of the ground state energies were obtained by the DMC simulations. The small statistical error allowed us to determine the quality of the assumed pseudopotentials by comparison of the DMC results with experimental values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460849
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  • 2
    Electronic Resource
    Electronic Resource
    Path integral Monte Carlo study of SF6-doped helium clusters (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 2341-2348 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The path-integral Monte Carlo technique is applied to study the SF6He39 cluster at low temperatures. The method employs as input only pair potentials, the number of atoms, and the temperature, and is thus independent of the trial function bias which can affect calculation of structural quantities in variational and diffusion Monte Carlo. We thereby obtain an unambiguous answer to the question of the location of SF6 in small clusters (39 He atoms), as well as the temperature dependence of the cluster structure. The cluster is found to undergo a gradual transition to a superfluid between 0.625 K and 1.25 K, and to evaporate significantly at temperatures above 2 K. We also calculate spectral shifts for the ν3 vibrational mode of SF6, using the instantaneous dipole-induced dipole mechanism. The results are compared with infra-red absorption measurements and with the previous ground-state quantum Monte Carlo calculations. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470929
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  • 3
    Electronic Resource
    Electronic Resource
    Generation of pseudopotentials from correlated wave functions (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 8169-8177 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The density matrix, or equivalently the natural orbitals play an essential role in determining the transferability of pseudopotentials to all orders of perturbation theory. In this work the one-particle density matrix and natural orbitals of Li, C, and Ne atoms are obtained using variational and diffusion Monte Carlo. Using these a pseudopotential is computed for the lithium atom.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466811
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  • 4
    Electronic Resource
    Electronic Resource
    Quantum mechanical simulation of liquids (1985)
    s.l. : American Chemical Society
    Accounts of chemical research 18 (1985), S. 268-273 
    Details
    ISSN: 1520-4898
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ar00117a002
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  • 5
    Electronic Resource
    Electronic Resource
    Path integral Monte Carlo applications to quantum fluids in confined geometries (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 10111-10118 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Path integral Monte Carlo is an exact simulation method for calculating thermodynamic properties of bosonic systems. Properties such as superfluidity and bose condensation are directly related to multiparticle exchange cycles of individual particle paths. Such calculations of bosonic systems in confined geometries, such as helium and hydrogen on surfaces and in droplets are reviewed. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1418443
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  • 6
    Electronic Resource
    Electronic Resource
    Density fluctuations in liquid4He. Path integrals and maximum entropy (1996)
    Springer
    Journal of low temperature physics 104 (1996), S. 339-357 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We estimate the dynamic structure factorS(q, ω) for liquid4He in both its normal and superfluidphases. A path integral Monte Carlo simulation is performed to compute the imaginary-time polarization propagatorF(q, τ), from whichS(q, ω) is extracted by maximum entropy. Results for normal4He are in good quantitative agreement with recent neutron scattering experimental data; broad agreement is found for superfluid4He as well, though sharp features are lost, particularly at lowq. We attribute the excessive smoothness of the results to the entropic “prior probability” function used in the maximum entropy reconstruction. The experimentally observed ground state excitation spectrumE(q) is accurately reproduced in the 0⩽q⩽2.5 Å−1 range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00751861
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  • 7
    Electronic Resource
    Electronic Resource
    Path integral Monte Carlo simulations of thin4He films on a H2 surface (1992)
    Springer
    Journal of low temperature physics 89 (1992), S. 581-584 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The adsorption of 4 He films for coverages from1/4 to3 monolayers ona H2 surface at low temperatures is studied with Path Integral Monte Carlo. We calculate the binding energy per 4 He atom to the substrate, density profiles of 4 He and H2, zero point motion of 4 He and H2, and the superfluid density of 4 He.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00694092
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  • 8
    Electronic Resource
    Electronic Resource
    Path integral monte carlo simulations of thin4He films on a H2 surface (1994)
    Springer
    Journal of low temperature physics 94 (1994), S. 185-217 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Atomatically thin4He films of up to three monolayers on molecular hydrogen (1,1,1) surfaces are studied at T = 0.5 K, using path integral Monte Carlo. We compute the binding energy of4He to the H2 substrate as a function of4He coverage and obtain evidence of the prewetting transition. Density profiles perpendicular to the4He-H2 interface are obtained, as well as the zero point motion and effective mass of4He parallel to the substrate surface. The superfluid density of4He vs. coverage is calculated, and the intermediate scattering function is computed, from which we estimate the speed of third sound. Finally, we calculate the vorticity-vorticity correlation function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00755424
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  • 9
    Electronic Resource
    Electronic Resource
    Path integral monte carlo simulations of H2 surfaces (1994)
    Springer
    Journal of low temperature physics 94 (1994), S. 161-183 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The (1,1, 1)-surfaces of bulk solid molecular hydrogen have been studied at temperatures between 0.5 K and 1.3 K, using path integral Monte Carlo. A general method is introduced for constructing an external potential to represent the tail correction for an arbitrary heterogeneous layered bulk substrate-adsorbate system. We compute density profiles parallel and perpendicular to the free H2 surface, total energies, and the surface tension. The structure of partial (not completely filled) surface layers is investigated and found liquid for some filling fractions. Quantum exchange of H2 molecules at the free surface is observed and the possibility of superfluidity in a surface layer of H2 is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00755423
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  • 10
    Electronic Resource
    Electronic Resource
    Path integral Monte Carlo simulations of the melting of molecular hydrogen surfaces (1996)
    Springer
    Journal of low temperature physics 102 (1996), S. 275-305 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have used Path Integral Monte Carlo to study the surface melting of molecular hydrogen. Density profiles perpendicular and parallel to the bare H2 surface are computed showing the formation of a liquid adlayer at 6 K, less than half the bulk melting temperature of para-hydrogen, 13.8 K. To estimate the onset temperature and depth of H2 surface melting we determine the static structure factor within the individual H2-layers for wave vectors in the plane and find no crystalline order down to 3 K in a partially filled H2 adlayer at the free surface. We find quantum effects amplify the melting point depression at the free H2 surface compared to bulk by a factor of five over classical Lennard-Jones solids and find that the zero-point fluctuations of molecules at the surface are much enhanced over their bulk values. We see vacancy formation in the solid before melting.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00754663
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