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  • 1
    Electronic Resource
    Electronic Resource
    The solvation of chloride by methanol—surface versus interior cluster ion states (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 9516-9526 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A combined experimental and theoretical structural study of methanolated chloride anions has been conducted, utilizing infrared vibrational spectroscopy and ab initio electronic structure calculations. These results represent the first such study for an anion with a nonaqueous solvent. The principal question addressed is whether the cluster ions assume structures reflecting surface or interior solvated states. The vibrational spectra in the O–H stretching regions, for Cl−(CH3OH)1–8,10,12, and calculated O–H vibrational bands for Cl−(CH3OH)1–4, consistently indicate that the chloride anion undergoes surface solvation. The behavior is remarkably similar to that of hydrated anions (chloride, bromide, and iodide) with large polarizabilities. This suggests that the asymmetric hydration of these anions lies not necessarily in the nature of the solvent, but in the nature of the anion. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478916
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  • 2
    Electronic Resource
    Electronic Resource
    Exploiting temporal nonlocality to remove scaling bottlenecks in nonadiabatic quantum dynamics (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 4134-4140 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An extension of the full multiple spawning (FMS) method for quantum non-adiabatic dynamics that capitalizes on the global nature of quantum mechanics and on the deterministic nature of the FMS method is discussed. The FMS method uses a classically motivated time-dependent basis set for the wave function and here we demonstrate that the choice of a temporally nonlocal basis set can reduce the scaling of the dominant effort in ab initio multiple spawning from O(N2) to O(N), where N is the number of basis functions describing the nuclear degrees of freedom. The procedure is applied to a two-dimensional two electronic state model problem and we show that the temporally nonlocal basis set provides accurate expectation values and branching ratios over a broad range of energies. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478297
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  • 3
    Electronic Resource
    Electronic Resource
    Nonadiabatic molecular dynamics: Validation of the multiple spawning method for a multidimensional problem (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 7244-7257 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The recently introduced full multiple spawning (FMS) method for molecular dynamics beyond the Born–Oppenheimer approximation is tested against exact numerical solution of the coupled nuclear Schrödinger equation for a two-dimensional model problem with two electronic states. The method uses a multiconfigurational frozen Gaussian ansatz for the wave function and the key idea is to expand the size of the basis set only during nonadiabatic events, using available information to predict the regions of phase space where population will be created. This is accomplished via the spawning procedure which keeps the basis size manageable while ensuring that it provides a reasonable approximation to the exact wave function. The parameters that govern the numerical accuracy of the method are discussed in detail. Expectation values and branching ratios are predicted quantitatively over a broad range of energies. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476142
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  • 4
    Electronic Resource
    Electronic Resource
    A multiple spawning approach to tunneling dynamics (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 6113-6121 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Quantum mechanical tunneling effects are investigated using an extension of the full multiple spawning (FMS) method. The FMS method uses a multiconfigurational frozen Gaussian ansatz for the wave function and it allows for dynamical expansion of the basis set during the simulation. Basis set growth is controlled by allowing this expansion only when the dynamics signals impending failure of classical mechanics, e.g., nonadiabatic and/or tunneling effects. Previous applications of the FMS method have emphasized the modeling of nonadiabatic effects. Here, a new computational algorithm that accounts for tunneling effects is introduced and tested against exact solution of the Schrödinger equation for two multi-dimensional model problems. The algorithm first identifies the tunneling events and then determines the initial conditions for the newly spawned basis functions. Quantitative agreement in expectation values, tunneling doublets and tunneling splitting is demonstrated for a wide range of conditions. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481213
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  • 5
    Electronic Resource
    Electronic Resource
    Ab initio/interpolated quantum dynamics on coupled electronic states with full configuration interaction wave functions (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 1376-1382 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a new approach to first-principles molecular dynamics that combines a general and flexible interpolation method with ab initio evaluation of the potential energy surface. This hybrid approach extends significantly the domain of applicability of ab initio molecular dynamics. Use of interpolation significantly reduces the computational effort associated with the dynamics over most of the time scale of interest, while regions where potential energy surfaces are difficult to interpolate, for example near conical intersections, are treated by direct solution of the electronic Schrödinger equation during the dynamics. We demonstrate the concept through application to the nonadiabatic dynamics of collisional electronic quenching of Li(2p). Full configuration interaction is used to describe the wave functions of the ground and excited electronic states. The hybrid approach agrees well with full ab initio multiple spawning dynamics, while being more than an order of magnitude faster. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478027
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  • 6
    Electronic Resource
    Electronic Resource
    Classical/quantal method for multistate dynamics: A computational study (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 2847-2856 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We discuss a classically-motivated method for modeling ultrashort laser pulse optical excitation. The very same method can be used to treat the breakdown of the Born–Oppenheimer approximation. The results are compared to numerically-exact quantum mechanics for a model problem representing excitation from the X (ground) state to the B (excited) state of molecular iodine. Expectation values and final B state populations are predicted quantitatively. The method provides a new way to simulate pump–probe experiments in particular and multistate dynamics in general. The method appears extendible to multidimensional problems. We argue that the increase of effort with dimensionality will be similar to that encountered in classical mechanical simulations as opposed to the exponential scaling of numerically-exact quantum mechanical propagation techniques. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471108
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  • 7
    Electronic Resource
    Electronic Resource
    Pseudospectral Møller–Plesset perturbation theory through third order (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 3631-3638 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a formulation and implementation of Møller–Plesset perturbation theory in a pseudospectral framework. At the second-order level, the pseudospectral formulation is a formally a factor of N/n faster than conventional approaches, while the third order is formally faster by a factor of n, where N is the number of atomic orbitals and n is the number of occupied orbitals. The accuracy of the resulting energies is probed for a number of test cases. Practical timings are presented and show conclusively that the pseudospectral formulation is faster than conventional ones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466350
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  • 8
    Electronic Resource
    Electronic Resource
    Erratum: Pseudospectral full configuration interaction [J. Chem. Phys. 97, 1876 (1992)] (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 4238-4238 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466235
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  • 9
    Electronic Resource
    Electronic Resource
    Pseudospectral double excitation configuration interaction (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 7081-7085 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a pseudospectral formulation of the single reference, closed shell double excitation configuration interaction method using a generator state self-consistent electron pair approach. The method scales as O(n2N3), compared to the conventional scaling of O(n2N4+n3N3). In no case tested does the pseudospectral energy differ by more than 0.35 mhartree from the conventional result.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464751
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  • 10
    Electronic Resource
    Electronic Resource
    Pseudospectral full configuration interaction (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 1876-1880 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A pseudospectral formulation of the full configuration interaction method is presented in this paper. This represents the first application of the pseudospectral approximation to configuration interaction expansions. It is shown that a formal scaling advantage of n, the number of molecular orbital basis functions, is achieved. The spectral and pseudospectral total energies obtained for a series of first-row atoms and ions are compared. The relative operation counts of the spectral and pseudospectral methods are also discussed in this paper. Finally, two hybrid spectral/pseudospectral approximations that vastly improve the accuracy of the pseudospectral total energies are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463176
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