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  • 1
    Electronic Resource
    Electronic Resource
    Analysis of the molecular density (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 4213-4220 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The minimal deformation criterion, previously proposed for the partition of the molecular density into atomic contributions, is updated and extended. For any Gaussian basis set, these atomic contributions are expanded in a series of real spherical harmonics by radial factors. The terms with l=0 determine the spherical parts of the atomic clouds and the remaining ones, their deformations. This detailed description is complemented with a simplified representation of the molecular density in terms of atomic charges and multipoles. Moreover, these descriptions give a simple way to calculate the electrostatic potential of the molecule as well as the electrostatic interaction between molecules. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478303
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  • 2
    Electronic Resource
    Electronic Resource
    Molecular integrals with Slater basis. V. Recurrence algorithm for the exchange integrals (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 9807-9816 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The numerical and analytical procedures, used for calculating exchange integrals with Slater functions, fail to give high accuracy for large quantum numbers and some values of the parameters. We propose here an algorithmic approach based on recurrence relations which start from some simple functions. An extensive study in which exponents, interatomic distances, and quantum numbers were varied proves that the new procedure is fully reliable. Finally, the cost of the procedure is analyzed, including the effect of the number of terms needed to attain a given accuracy. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467946
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  • 3
    Electronic Resource
    Electronic Resource
    Neutron scattering and magnetic susceptibilities of dilute PtCo alloys calculated by Monte Carlo methods (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3617-3619 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Neutron scattering experimental data for dilute PtCo alloys show sharp forward peaks indicating the inhomogeneous distribution of magnetization in these alloys and the size and shape of magnetization clouds. These characteristics of the clouds, however, do not agree with those obtained by magnetization measurements. The disagreement suggests an important nonelastic contribution to such scattering. We, therefore, calculated the diffuse neutron cross sections for these alloys employing a magnetic environment model for the magnetization clouds, that has been used successfully for other giant moment dilute alloys such as PdFe and PtFe. The calculations were made by Monte Carlo methods for alloys of PtCo in the concentration region 1.0≤c≤6.0 at. %Co. The results show sharp peaks due to quasielastic scattering which reproduce well the experimental neutron data. We also calculated by the same methods the magnetic susceptibilities for alloys of PtCo with c〈1.0 at. %Co. The results show a good agreement with experimental data. The validity of the model and of the magnetic correlations used for the calculations is supported by their agreement with experimental results. At high concentrations the model should not apply as the clouds are considered independent in the calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340713
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  • 4
    Electronic Resource
    Electronic Resource
    Magnetism of RhN clusters (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4906-4908 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The size and structural dependence of the magnetic properties of RhN clusters (3≤N≤27) are studied by using a d-electron tight-binding Hamiltonian which includes hybridizations, Coulomb interactions, and spin–orbit coupling on the same electronic level. We show that the spin (S) and orbital (L) magnetic moments depend strongly on the local environment of the atoms and that their behavior as a function of the cluster size present oscillations which are in good qualitative agreement with experiment. The magnetic anisotropy energy and the anisotropy in L are quantified by considering different directions of the spin magnetization S within the cluster. We conclude that orbital contributions to the average magnetization in RhN clusters could be important for precise comparison with experiment. Bond-length relaxation effects are also briefly discussed. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373198
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  • 5
    Electronic Resource
    Electronic Resource
    Simultaneous observation of Barkhausen pulses and jumps in resistance fluctuations in ferromagnetic materials (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 171-174 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An experimental setup which simultaneously registers induced Barkhausen pulses and short time variations in electrical resistance has been developed. The skin effect associated with the use of an alternating current of 100 kHz reduces the volume of the sample which is sensitive to the passing of the current, making it possible to detect the rapid modifications in resistance in a standard Ni thermocouple wire subjected to a slowly varying magnetic field. The combination of both techniques clearly shows the association between jumps in resistance and the dynamics of some magnetic domains. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149560
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  • 6
    Electronic Resource
    Electronic Resource
    Application of a sine transform method to experiments of single-photon-decay spectroscopy: Single exponential decay signals (1992)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 63 (1992), S. 3268-3273 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In this article we present as an experiment in single-photon-decay spectroscopy an alternative method to that based on the measurement of the probability distribution function, Pf(t), of the time intervals for the time of arrival of the first photon after the excitation pulse. We propose the measurement of the sine transform of Pf(t), which gives a maximum when the fluorescence signal is of the single exponential decay type. The existence of this maximum allows us to determine very accurately the value of the decay constant using a number of measurements which is lower than that required to establish a Pf(t) that is accurate enough to draw the same conclusions. A theoretical model of the error is studied and is compared by means of a computer simulation with the usual method of measuring Pf(t). An experiment is performed using a TMMC crystal to verify the validity of the theoretical predictions and of the simulation results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142535
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  • 7
    Electronic Resource
    Electronic Resource
    Preparation and transport properties of polycrystalline Bi and Bi–SiO2 nanocomposites (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 88 (2000), S. 3269-3275 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Bismuth–silica nanocomposites and polycrystalline bismuth were prepared via powder metallurgy in order to study the influence of silica inclusions on the thermoelectric properties of bismuth. Bi–SiO2 powders containing from 0.5 to 15 vol. % of silica and pure Bi powders were produced by an arc-plasma processing. Transmission electron microscopy investigations revealed the presence of a nanometric silica shell around the Bi grains. The powders were cold pressed and sintered close to the melting temperature of bismuth. The bulk microstructures are very different for the bismuth and the Bi–SiO2 nanocomposites because silica, which is primarily dispersed at grain boundaries, inhibits the grain growth during sintering. The electrical resistivity was measured from 5 to 300 K, while the thermoelectric power and the thermal conductivity were measured from 65 to 300 K on both polycrystalline bismuth and Bi–SiO2 samples containing 0.5, 4, and 15 vol. % of silica, respectively. The transport properties are mainly discussed with regard to the microstructures. In spite of a strong reduction of the thermal conductivity for the nanocomposites, the thermoelectric figure of merit is not improved compared to bismuth due to a dominating concurrent increase of the electrical resistivity resulting from a finite-size effect. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1289079
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  • 8
    Electronic Resource
    Electronic Resource
    Calculation of the magnetic properties of CoN clusters on Pd(111) (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 4894-4896 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic properties of CoN clusters (N≤7) deposited on Pd(111) have been determined in the framework of a self-consistent d-band model Hamiltonian. Results are given for the spin and orbital magnetic moments and for the magnetic anisotropy energy for different structures of the CoN clusters. We find that the magnetic orbital contribution to the total magnetic moment can be of the order of 20%. The magnetization direction of CoN changes in most cases from in-plane to off-plane upon deposition. We observe that the main contribution to the magnetic anisotropy energy results from the cluster–substrate interface. Comparison of the magnetic properties between deposited and free clusters is also provided. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.373194
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  • 9
    Electronic Resource
    Electronic Resource
    Recurrence relations for the expansion of Slater-type orbitals about displaced centers (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5890-5894 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We show here that the coefficients for the expansion of any Slater-type function over a displaced center can be obtained by three simple (and numerically stable) recurrence relations starting at the expansion coefficients of the 1s or 2s orbitals. We present also compact (and very fast to compute) formulas for these initial quantities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451551
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  • 10
    Electronic Resource
    Electronic Resource
    Density and binding forces in diatomics (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 1788-1799 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In a recently reported method, the molecular density is partitioned in minimally deformed atomic contributions, which are expanded in spherical harmonics times radial factors. Here we use this representation to express the electrostatic potential of the molecule, the force on its nuclei, and the conformational variations of energy in terms of some simple integrals of the atomic radial factors. As a first application, we analyze the relationship between the density and the binding forces (and the bonding energy) in the diatomic molecules of the first row atoms. Two types of forces act on each nucleus: the self-pulling exerted by its own cloud and the external force due to the remaining atoms. The self-pulling comes only from the dipole type term of the atomic density. The external force comes from the other clouds and nuclei and is dominated by the effective charges which depend on the outermost region of the charge term. Analyzing the progressive deformations of the atoms when they approach each other, the forces associated with these deformations and their contributions to the energy, one has a detailed description of the chemical bond which is complementary, and in many aspects more appealing, than the conventional ones. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1420403
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