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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 9395-9404 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A detailed discussion of an approximate, variational approach to atom–molecule reactive scattering is presented. This approach reduces the formally three arrangement atom–diatomic molecule reactive scattering problem to one of a single arrangement without the use of negative imaginary potentials at the exit channel boundaries. The method is based on applying the Kohn variational principle for the log-derivative matrix to a representation of the scattering wave function that spans just the reactant arrangement. For many reactive systems, the method yields impressively accurate results for total reaction probabilities from a specific initial state. In such cases, it is also possible to extract fairly accurate state-resolved reaction probabilities from the results of the variational calculation. The mathematical and practical aspects of accomplishing this are presented. We evaluate the advantages and the limitations of the method by numerical computations on the collinear H+H2 (and isotopes) and F+H2, and the three dimensional (J=0) F+H2 reactions. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 2953-2967 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a method for including the geometric phase in quantum reactive scattering computations based on the log derivative version of the Kohn variational principle. A new variational functional is developed which includes the influence of the geometric phase through modifications in the momentum operators. The system investigated is a two-dimensional reactive scattering model which includes the vector potential induced by the magnetic field of an infinitely long solenoid. The coordinates used in this model are analogous to Jacobi coordinates used in atom–diatom systems. Some interesting features of this study include the gauge invariance of the scattering probabilities, symmetry adaptation of the wave function, and the behavior of the probability density in the presence of the geometric phase.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 2354-2364 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An algorithm for calculating rotation–vibrational energy levels and wave functions for AB–CD tetra-atomic systems is presented. By transforming the wave equation into a large sparse eigenvalue problem, we can take advantage of the implicitly restarted Lanczos method developed by Sorensen and co-workers. The algorithm has been applied to calculations of the lowest 40 bound states of (HF)2, (DF)2 and HF⋅DF with even and odd parities. The lowest 40 energies and corresponding wave functions for (HF)2 with J=0 and even parity can be calculated in 10.5 minutes on 126 processors of a CRAY T3E. The resulting energy levels are found to be in excellent agreement with the previously reported values of Zhang, et al. [J. Chem. Phys. 102, 2315 (1995)]. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 2365-2375 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Results of a six-dimensional treatment of the rotation–vibration Hamiltonian for (HF)2 are presented. Energies of 40(J+1) states for J≤4 are reported. These energies and the corresponding wave functions are used to analyze rotation–vibration interactions in (HF)2. Over the range of energies probed in this study, Coriolis couplings are found to be relatively unimportant and for 94% of the states the wave functions and energies can be approximated by the solutions to a Hamiltonian in which the Coriolis coupling terms are neglected. Rotation–vibration interactions are investigated in greater detail for the ground state and for states with one and two quanta of excitation in the intermolecular stretching vibration ν4. Specifically, we study the K and n4 dependencies of the tunneling splitting and the effective rotational constant that corresponds to rotation about the intermolecular axis. Based on an analysis of the wave functions and the potential, we find that the observed trends can be attributed to the fact that (HF)2 behaves like a quasilinear molecule whose large amplitude bending motions lead to significant wave amplitude in linear configurations, even in the vibrational ground state. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 3460-3470 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Experimental data from vibrationally and rotationally resolved laser induced fluorescence experiments have been used to produce potential energy surfaces (PES) for the excited A˜ 2Σ+ states of the Ar⋅SH and Kr⋅SH van der Waals complexes. This was done using a potential energy functional form first suggested by Bowman and co-workers [J. Phys. Chem. 94, 2226, 8858 (1990); Chem. Phys. Lett. 189, 487 (1992)] for Ar⋅OH/D. A discrete variable representation (DVR) of the vibration–rotation Hamiltonian was used in combination with the implicitly restarted Lanczos method and sequential diagonalization truncation (SDT) of the DVR Hamiltonian. This approach takes advantage of the sparseness of the DVR Hamiltonian and the reduced order of the SDT representation. This combination of methods greatly reduces the amount of computational time needed to determine the eigenvalues of interest. This is important for the determination of the PES that results from minimizing the difference between the experimental and theoretically predicted values for the vibronic energy levels and their corresponding rotational constants. In addition this procedure was helpful in assigning the absolute vibrational quantum numbers for the deuterated species for which less experimental data was available. Plots of the calculated wavefunctions corresponding to various experimentally vibronic bands indicate that these states sample regions of the PES from 0 degrees, where the hydrogen atom is closest to the rare gas atom, to approximately the saddle point, near the T-shaped configuration. As a result this region of the surface is determined accurately whereas the region of the PES around 180 degrees, corresponding to the sulfur atom being closest to the rare gas atom, is determined only qualitatively. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 2705-2719 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An efficient parallel algorithm is reported for determining all bound rovibrational energy levels for the HO2 molecule for nonzero angular momentum values, J=1, 2, and 3. Performance tests on the CRAY T3D indicate that the algorithm scales almost linearly when up to 128 processors are used. Sustained performance levels of up to 3.8 Gflops have been achieved using 128 processors for J=3. The algorithm uses a direct product discrete variable representation (DVR) basis and the implicitly restarted Lanczos method (IRLM) of Sorensen to compute the eigenvalues of the polyatomic Hamiltonian. Since the IRLM is an iterative method, it does not require storage of the full Hamiltonian matrix—it only requires the multiplication of the Hamiltonian matrix by a vector. When the IRLM is combined with a formulation such as DVR, which produces a very sparse matrix, both memory and computation times can be reduced dramatically. This algorithm has the potential to achieve even higher performance levels for larger values of the total angular momentum. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Hearing sensitivity in mammals is enhanced by more than 40 dB (that is, 100-fold) by mechanical amplification thought to be generated by one class of cochlear sensory cells, the outer hair cells. In addition to the mechano-electrical transduction required for auditory sensation, ...
    Type of Medium: Electronic Resource
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