ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

X
feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
  • 1
    Electronic Resource
    Electronic Resource
    An effective centroid Hamiltonian and its associated centroid dynamics for indistinguishable particles in a harmonic trap (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 4808-4818 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We show that incorporating the effects of Bose–Einstein or Fermi–Dirac quantum statistics within the centroid molecular dynamics formalism leads to additional correlations in the system due to exchange effects. In the case of Bose–Einstein statistics they appear as an additional attraction between physical particles while an additional repulsion is observed for Fermi–Dirac statistics. We show that we can account for these correlations through the effective centroid Hamiltonian. Within the approach based on the phase space centroid density, this Hamiltonian depends on centroid momenta in a nonclassical way. We illustrate the above findings using a simple model of two bosons and fermions in a harmonic potential. The average of a centroid variable along centroid trajectories based on such an effective Hamiltonian can be used to study the equilibrium properties of quantum systems. Is is also shown that the dynamics of the centroid variables derived from the quantum mechanical dynamics of the corresponding physical observables does not depend on exchange effects for a harmonic system. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1449868
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 2
    Electronic Resource
    Electronic Resource
    Operator formulation of centroid dynamics for Bose–Einstein and Fermi–Dirac statistics (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 7822-7831 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper is devoted to the development of an operator formulation of the recent extension of the centroid molecular dynamics method [J. Chem. Phys. 110, 3647 (1999); 111, 5303 (1999)] to boson and fermion systems. An operator calculus is used to rederive the basic equations of centroid dynamics. The following generalization to the case of systems of many indistinguishable particles is based on the use of a projection operator. Two different definitions of the quasi-density operator for bosonic and fermionic systems are suggested. The first definition allows an exact evaluation of equilibrium properties for systems with exchange effects using classical-like molecular dynamics calculations. The second one provides a formal justification of Bose–Einstein/Fermi–Dirac centroid dynamics with the same set of approximations as for Boltzmann statistics, and can be used to extract quantum dynamical information. In this case, the corresponding centroid correlation function can be related to a double Kubo transformed quantum mechanical one. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1407291
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Path integral formulation of centroid dynamics for systems obeying Bose–Einstein statistics (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 4484-4495 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper presents a formal foundation for the recent extension [J. Chem. Phys. 110, 3647 (1999)] of the centroid molecular dynamics (CMD) method to systems obeying Bose–Einstein statistics. It is shown that the introduction of centroid phase space coordinates corresponding to individual physical particles allows one to obtain (exact) canonical averages within the framework of the bosonic CMD method. It is also shown that formally exact expressions for quantum mechanical Kubo transformed correlation functions can be written in terms of individual particle centroids and that a CMD approximation can be introduced. Calculations for a bosonic trimer are used as an illustration of the new concepts introduced in this work. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1392355
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 4
    Electronic Resource
    Electronic Resource
    A Feynman path centroid dynamics approach for the computation of time correlation functions involving nonlinear operators (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 919-929 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The centroid dynamics formalism is extended to the calculation of time correlation functions of nonlinear operators. It is shown that centroid correlation functions can be related to quantum mechanical ones via higher order Kubo-type transforms. A key step is the construction of the correlation functions from a mixed classical/semiclassical centroid representation of the operators. A general methodology is developed to relate these Kubo-type transforms to the desired quantum correlation functions. The approach is tested using a one-dimensional anharmonic potential for which the 〈x2x2(t)〉 and the 〈x3x3(t)〉 correlation functions are computed. Applications of this new approach are also outlined. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481872
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 5
    Electronic Resource
    Electronic Resource
    Time-dependent Hartree approaches for the study of intramolecular dynamics in dimer systems (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 10778-10786 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We apply and the time-dependent Hartree (TDH) method to the study of intramolecular dynamics in dimer systems. The HCl dimer is chosen as test case. Model calculations are performed on reduced dimensional representation of this system namely two-, three-, and four-dimensional ones. We assess the validity of different implementations of the TDH method including the account of direct correlations between coordinate pairs, and mixed quantum-classical and quantum-Gaussian wave packets treatments. The latter yields very good results compared to the fully quantal treatment. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481722
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 6
    Electronic Resource
    Electronic Resource
    The structure of Nb3O and Nb3O+ determined by pulsed field ionization–zero electron kinetic energy photoelectron spectroscopy and density functional theory (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5335-5342 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The geometrical structures of the ground states of triniobium monoxide, Nb3O, and its cation, Nb3O+, have been determined by an experimental and theoretical study. Vibrationally resolved photoelectron spectra of an Nb3O cluster beam were obtained at 100 and 300 K using the pulsed field ionization-zero electron kinetic energy technique. The spectra were simulated by calculating multidimensional Franck–Condon factors using the geometries and harmonic vibrational frequencies obtained from density functional theory for the minimum energy structures of the ion and neutral molecule. The rather remarkable agreement between the experiment and the simulated spectra establishes that Nb3O and Nb3O+ have planar C2v structures with the oxygen atom bridging two niobium atoms. These are the most complex transition metal cluster structures to date to be characterized by gas phase spectroscopic techniques. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470568
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 7
    Electronic Resource
    Electronic Resource
    An evaluation of methods designed to calculate energy levels in a selected range and application to a (one-dimensional) Morse oscillator and (three-dimensional) HCN/HNC (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5600-5612 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this paper we study three methods designed to calculate energy levels in a range of interest. The methods are applied to a one-dimensional (1-D) Morse oscillator and to HCN/HNC (in three-dimensions). Energy levels in the chosen range are computed using the filter-diagonalization method proposed by Neuhauser [J. Chem. Phys. 93, 2611 (1990)], a spectral transform Lanczos method, and a guided Lanczos method we suggest in this paper. In the guided Lanczos method convergence of the energy levels of interest is favored by choosing the Lanczos starting vector so that it has a substantial overlap only with eigenvectors of the eigenvalues in the chosen range. This biased starting vector is calculated from a solution of the time-dependent Schroedinger equation. Of the three methods the guided Lanczos is the most efficient for both the Morse oscillator and HCN/HNC. None of the methods designed to favor a chosen energy range are, however, (for the two problems we considered) as efficient as a straightforward Lanczos method (without an optimized starting vector). © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470543
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 8
    Electronic Resource
    Electronic Resource
    Feynman path centroid dynamics for Fermi–Dirac statistics (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 5303-5305 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this communication the centroid molecular dynamics (CMD) method is tested for systems of fermions using a modified version of the expression for the fermion Feynman path centroid density derived in a recent publication [J. Chem. Phys. 110, 3647 (1999)]. The method is applied to a model system consisting of two noninteracting fermions in an anharmonic potential well and the position autocorrelation function is computed. The exact fermion position autocorrelation function exhibits a longer period of oscillation when compared to the bosonic case. This shift is due to the anharmonic nature of the given potential function where the level spacing decreases with the increase of energy. The CMD results agree very well with the exact quantum mechanical results for this example. This indicates, along with the previous results on a boson system, that quantum statistics can in principle be incorporated into the CMD method without any degradation of the accuracy of the approximation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479789
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 9
    Electronic Resource
    Electronic Resource
    Vibrational and geometric structures of Nb3C2 and Nb3C+2 from pulsed field ionization-zero electron kinetic energy photoelectron spectra and density functional calculations (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 10663-10671 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibrational frequencies of three niobium normal modes of triniobium dicarbide neutral and cation have been determined from pulsed field ionization-zero electron kinetic energy photoelectron spectra. The niobium stretching mode has a frequency of 326 cm−1 in the neutral and 339 cm−1 in the ion. The two deformation modes have frequencies of 238 and 82 cm−1 in the neutral and a degenerate frequency of 258 cm−1 in the ion. The geometry of the triniobium dicarbide has been established by comparing the experimental spectra with theoretical calculations. The cluster has a trigonal bipyramid geometry with carbon atoms capping on each face of the metal frame. The cation cluster has D3h symmetry whereas the neutral cluster has lower symmetry resulting from a Jahn–Teller distortion. A second low-lying structure with doubly bridging carbon atoms has been identified by the calculations but has not yet been observed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472873
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
  • 10
    Electronic Resource
    Electronic Resource
    On the Feynman path centroid density for Bose-Einstein and Fermi-Dirac statistics (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 3647-3652 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Expressions are derived for the Feynman path centroid density of systems of identical particles, namely, Bosons and Fermions. The resulting expressions are applied to a system of two independent particles in a quartic oscillator and the corresponding centroid densities are computed, plotted and compared to the distinguishable particle case. In regions where the particle centroids are close to each other, the Boson centroid density displays an enhanced amplitude in comparison to the distinguishable case. This behavior is attributed to the attractive correlations in Boson systems. The Fermion centroid density, however, can have the peculiar property of being negative in those regions where the particle centroids are in close proximity. This feature is related to the Pauli exclusion principle. This property of the Fermion centroid density rules out its strict interpretation as a probability distribution. Equilibrium properties such as the canonical partition function and the average position were accurately computed using both densities. The Boson density was also used to compute the position autocorrelation function using the Centroid Molecular Dynamics method and the results are in excellent agreement with those of an exact quantum calculation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478254
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...