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  • 1
    Electronic Resource
    Electronic Resource
    Non-Born–Oppenheimer calculations on the LiH molecule with explicitly correlated Gaussian functions (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 3393-3397 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the first ever non-Born–Oppenheimer variational calculations on the ground state of a four electron molecular system. The basis set used in the calculations consists of explicitly correlated Gaussians multiplied by powers of the internuclear distance. To accelerate the optimization of the many nonlinear variational parameters involved in the variational wave function, we performed the calculations on a cluster of Linux workstations using MPI and a parallel implementation of the formulas. Results for the nonadiabatic ground state energy of LiH, as well as expectation values for the kinetic and potential energies, the internuclear and square of the internuclear distance, the virial coefficient, and the square of the energy gradient norm are reported. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1342757
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  • 2
    Electronic Resource
    Electronic Resource
    High accuracy non-Born–Oppenheimer calculations for the isotopomers of the hydrogen molecule with explicitly correlated Gaussian functions (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 4203-4205 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The first rigorous, variational results for the nonadiabatic (i.e., non-Born–Oppenheimer) ground states of the six isotopomers of the hydrogen molecule are reported. Ground-state energies in Hartrees are: H2[−1.164 025 023 2] [this result was reported by us earlier in Phys. Rev. Lett. 83, 2541 (1999)], D2[−1.167 168 78], T2[−1.168 535 65], HD[−1.165 471 906], HT[−1.166 002 033], and DT[−1.167 819 642]. Expectation values for the kinetic and potential energies, the internuclear distance and the square of the internuclear distance, the virial coefficient, and the square of the energy gradient norm for the optimized wave functions are also reported. The calculations were performed with a direct nonadiabatic variational approach using a new diatomic correlated Gaussian basis set exponentially dependent on interparticle distances and including pre-exponential powers of the internuclear distance. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1288376
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  • 3
    Electronic Resource
    Electronic Resource
    Geometry optimization in delocalized internal coordinates: An efficient quadratically scaling algorithm for large molecules (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 4986-4991 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using a Z-matrix-like approach for generating new Cartesian coordinates from a new geometry defined in terms of delocalized internal coordinates, we eliminate the costly O(N3) iterative back-transformation required in standard geometry optimizations using delocalized (or natural/redundant) internals, replacing it with a procedure which is only O(N). By replacing the gradient transformation with an iterative solution of a set of linear equations, we also reduce this step from O(N3) to roughly O(N2). This allows a very efficient method for geometry optimization of large molecules in internal coordinates. Several optimizations on systems containing up to 500 atoms are presented, comparing the performance of the new algorithm with its predecessor, and demonstrating the practical utility and efficiency of our approach. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478397
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  • 4
    Electronic Resource
    Electronic Resource
    Electron affinity of hydrogen, deuterium, and tritium: A nonadiabatic variational calculation using explicitly correlated Gaussian basis functions (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 4589-4595 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Nonadiabatic variational calculations for the anion ground state energies, mass shifts, and electron affinities of Hydrogen, Deuterium and Tritium are reported. Electron affinities values are 6083.0994, 6086.7137, and 6087.9168 cm−1 for Hydrogen, Deuterium, and Tritium, respectively. These results were obtained using a basis of explicitly correlated Gaussians. Exact nonrelativistic energy bounds are carefully predicted: E(H−)=−0.5 274 458 811, E(D−)=−0.5 275 983 247, and E(T−)=−0.5 276 490 482 in hartree energy units. It is shown that these new bounds cannot be obtained using the infinite nuclear mass approximation plus Rydberg scaling and the usual first order mass polarization correction. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473500
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  • 5
    Electronic Resource
    Electronic Resource
    A correlated basis set for nonadiabatic energy calculations on diatomic molecules (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 7166-7175 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new explicitly correlated basis set suitable for nonadiabatic energy calculation on small diatomic molecules is presented. The basis functions consist of correlated Gaussians multiplied by powers of the internuclear distance. N-body formulas for Hamiltonian matrix elements and energy gradient components are derived and presented along with a discussion of the nonadiabatic Hamiltonian and symmetry considerations. A sample calculation is presented for the ground state energy of the benchmark system H2+ in which rapid convergence to near exact results was observed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478620
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  • 6
    Electronic Resource
    Electronic Resource
    A new N-body potential and basis set for adiabatic and non-adiabatic variational energy calculations (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 8760-8768 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new functional form for multi-body expansions of potential energy surfaces and basis functions for correlated adiabatic and fully non-adiabatic variational energy calculations is presented. N-body explicitly correlated Gaussians with pre-multiplying factors consisting of products of powers of internal distance coordinates are utilized in a dual role to analytically represent isotropic potentials and energy eigen-functions in the same internal coordinate system. Practical aspects of this new methodology are presented. The ideas and methods are prototyped and illustrated with two simple diatomic examples; the Morse potential and an accurate H2 potential for which essentially exact results are obtained for vibrational energy levels. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.473936
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