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  • 1
    Electronic Resource
    Electronic Resource
    Correlated Monte Carlo wave functions for the atoms He through Ne (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 4172-4178 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We apply the variational Monte Carlo method to the atoms He through Ne. Our trial wave function is of the form introduced by Boys and Handy. We use the Monte Carlo method to calculate the first and second derivatives of an unreweighted variance and apply Newton's method to minimize this variance. We motivate the form of the correlation function using the local current conservation arguments of Feynman and Cohen. Using a self-consistent field wave function multiplied by a Boys and Handy correlation function, we recover a large fraction of the correlation energy of these atoms. We give the value of all variational parameters necessary to reproduce our wave functions. The method can be extended easily to other atoms and to molecules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458750
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  • 2
    Electronic Resource
    Electronic Resource
    Model Hamiltonians for atomic and molecular systems (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1003-1006 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model Hamiltonian, designed to allow larger systems to be treated with the Green's function Monte Carlo method, is introduced for atomic and molecular systems. The model reduces the statistical variance associated with Green's function Monte Carlo calculations by reducing potential energy fluctuations in the core regions. By performing calculations of Li, LiH, and Li2 we show that this method can be used to obtain energy differences with much less computer time than required for the complete interaction. Increases in efficiency for larger systems will be even greater.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456200
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  • 3
    Electronic Resource
    Electronic Resource
    The domain Green's function method (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 2868-2874 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An implementation of the domain Green's function Monte Carlo algorithm is described. Unlike the short time approximation, the method is variational and exact within the limits of the fixed node approximation. The systems investigated include LiH, Be in the ground and first excited states, a study of the C2v insertion pathway of Be into H2, and H2O. We predict a barrier of 0.190 hartree for the insertion reaction with a statistical accuracy of ±2%. Better than 90% of the correlation energy is recovered in each case, which makes these some of the most accurate computations to date.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451046
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  • 4
    Electronic Resource
    Electronic Resource
    Erratum: The domain Green's function method [J. Chem. Phys. 85, 2868 (1986)] (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 1906-1906 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453745
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  • 5
    Electronic Resource
    Electronic Resource
    A path integral ground state method (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 1366-1371 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ground state expectation values are obtained by using a path integral ground state Monte Carlo method. The method allows calculations of ground state expectation values without the extrapolations often used with Green's function and diffusion Monte Carlo methods. We compare our results with those of Green's function Monte Carlo by calculating some ground state properties of the van der Waals complex He2Cl2 as well as the infinite systems liquid and solid 4He. Advantages and disadvantages of the present method with respect to previous ones are discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481926
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  • 6
    Electronic Resource
    Electronic Resource
    Constraint dynamics for quantum Monte Carlo calculations (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 44-47 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We describe how to apply classical constraint dynamics to problems in diffusion Monte Carlo. We apply the method to rigid and nonrigid water molecules with an internal rotational degree of freedom. The method is applicable to a wide variety of problems. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481771
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  • 7
    Electronic Resource
    Electronic Resource
    Long range order in 2-D arrays of nanometer-sized Fe islands on CaF2/Si(111) (invited) (abstract) : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5056-5056 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effective magnetic moment was measured as a function of Fe island size during the initial stages of Fe growth on CaF2/Si(111) in an ultrahigh vacuum scanning electron microscope equipped with an in situ SMOKE analysis chamber. This substrate was selected for its wide bandgap, chemical inertness, viability of integration into an Si based technology and the availability of nanopatterning using electron beams for producing devices. Fe grown at room temperature initially nucleates into a monodisperse distribution of 3-D islands at very high nucleation densities (8×1012/cm2). Increased Fe coverages lead to 2-D island growth. A room temperature superparamagnetic to ferromagnetic phase transition occurs as a function of Fe island radius. Mean field and Monte Carlo calculations illustrate that three distinct magnetic phases exist as a function of island diameter. Ferromagnetic order is present at room temperature when r(approximately-greater-than)3 nm, superparamagnetism is favored when 2 nm 〈 r 〈3 nm, and a frustrated random antiferromagnetic phase exists when r〈2 nm. Further depositions of Ag on superparamagnetic Fe island arrays produce Ag islands which couple the covered Fe island moments in-plane, implying that the Ag mediates the magnetic exchange between individual Fe islands within an Ag island. Implications for 2-D giant magnetoresistance devices will be discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361570
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  • 8
    Electronic Resource
    Electronic Resource
    Correlated Monte Carlo wave functions for some cations and anions of the first row atoms (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 3382-3385 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We applied the variational Monte Carlo method to the computation of the correlation energy for several first row cations (Li+ through Ne+) and anions (B− through F−). In addition, we obtained estimates of their ionization potentials and electron affinities. The ionization potentials differ from the experimental results on the average by 0.11 eV and the electron affinites differ on the average by 0.07 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463938
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  • 9
    Electronic Resource
    Electronic Resource
    He2Cl2 and He3Cl2 van der Waals clusters: A quantum Monte Carlo study (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 6472-6480 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The results of the first variational and Green's function Monte Carlo calculations of the vibrational ground states of He2Cl2 and He3Cl2 van der Waals (vdW) clusters are presented in this paper. The quantum dynamics of all internal degrees of freedom are treated exactly. The ground state wave function of He2Cl2 is characterized by means of the probability distribution functions of the intermolecular degrees of freedom, which reveal an exceptionally fluxional vdW complex. A simple model for the ground state of HenCl2 vdW clusters was developed. The zero-point energies of He2Cl2 and He3Cl2 predicted by this model are in remarkable agreement (to within 0.6%) with the accurate results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463708
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  • 10
    Electronic Resource
    Electronic Resource
    Enhanced superparamagnetism in two-dimensional arrays of nanometer-sized Fe islands (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 2878-2880 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Iron grown on room-temperature CaF2/Si(111) substrates form two-dimensional arrays of nanometer-sized superparamagnetic islands. Deposition of Ag on the Fe/CaF2/Si(111) produced a superparamagnetic response where the effective moment was proportional to the number of Fe islands covered by an average-sized Ag island. The nonmagnetic Ag overlayer mediates a long-range exchange between neighboring Fe islands within an individual Ag island. Monte Carlo methods are used to examine ordering in two dimensions and to set minimum interisland coupling strengths. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114815
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