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  • 1
    Electronic Resource
    Electronic Resource
    Analytic energy gradients for general coupled-cluster methods and fourth-order many-body perturbation theory (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5143-5150 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Energy gradient equations are presented for the coupled-cluster model with all possible excitations. By taking advantage of the equations for the coupled-cluster amplitudes, the gradient formulas may be expressed without explicit reference to the first-order changes in the amplitudes, in contrast to all earlier work. The coupled-cluster doubles (CCD) and coupled-cluster singles, doubles, and triples (CCSDT) models are treated as special cases of the general theory. Finally, by limiting the model to finite orders in perturbation theory, the gradient equations for the full fourth-order many-body perturbation energy are derived. Like the fourth-order energy itself, the gradient procedure is shown to be an n7 process in the number of basis functions. The computational implementation of this fourth-order energy gradient is discussed in detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451823
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  • 2
    Electronic Resource
    Electronic Resource
    Development of transferable interaction models for water. II. Accurate energetics of the first few water clusters from first principles (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 1493-1499 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report accurate energetics for the water trimer through pentamer global ring minima and four low-lying hexamer isomers (cage, prism, book, cyclic S6) from first principles electronic structure calculations. The family of augmented correlation-consistent orbital basis sets of double through quintuple zeta quality was used in order to estimate complete basis set (CBS) limits for the cluster total association energies at the second order perturbation (MP2) level of theory. These are −15.8 kcal/mol (trimer), −27.6 kcal/mol (tetramer), −36.3 kcal/mol (pentamer), −45.9 kcal/mol (prism hexamer), −45.8 kcal/mol (cage hexamer), −45.6 kcal/mol (book hexamer), and −44.8 kcal/mol (ring S6 hexamer). Effects of higher correlation, estimated at the coupled cluster plus single and double with a perturbative estimate of the triple excitations [CCSD(T)] level of theory, as well as inclusion of estimates for core–valence correlation suggest that these estimates are accurate to within 0.2 kcal/mol. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1423941
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  • 3
    Electronic Resource
    Electronic Resource
    Occupational Health Guidelines for Control of Q Fever in Sheep Research (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 590 (1990), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1990.tb42234.x
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  • 4
    Electronic Resource
    Electronic Resource
    Orbital-invariant second-order many-body perturbation theory on parallel computers: An approach for large molecules (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 9582-9589 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The equations for the second-order many-body perturbation theory [MBPT(2)] energy are derived in an orbital-invariant representation, analogous to that obtained with the method of self-consistent electron pairs of Meyer. This formulation is well suited to take advantage of the localized nature of interactions in large chemical systems in order to reduce the computational effort required to study them. This formulation of the MBPT(2) method also lends itself to implementation on parallel computers. We describe a scalable implementation in which the key data are distributed across the parallel computer rather than being replicated. Portability to both shared- and distributed-memory computer architectures is provided through the use of a subroutine library implementing a "global array'' programming model. We demonstrate that this approach is scalable even for relatively small chemical systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468774
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  • 5
    Electronic Resource
    Electronic Resource
    Analytical calculation of full configuration interaction response properties: Application to Be (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 7479-7485 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The computation of the frequency dependent linear and quadratic response functions is formulated at the full configuration interaction (FCI) level of theory. It is demonstrated that the frequency dependent polarizability (for real and imaginary frequencies) may be obtained with quadratic dependence on the error in the solution of the response equations. An efficient solution of the FCI response equations for large imaginary frequencies is developed. Initial application is to the Be atom in the standard 9s9p5d basis. Reported results include transition energies and dipole moments for the first few singlet and triplet S, P, and D states, the first polarizability at real and imaginary frequencies, the C6 coefficient, and the static second hyperpolarizability. Comparison to prior theoretical results in this basis, and to experiment, is made where possible. It is the first time that many of these properties have been computed at the FCI level of theory for any system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461373
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  • 6
    Electronic Resource
    Electronic Resource
    Approximating full configuration interaction with selected configuration interaction and perturbation theory (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 5021-5031 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Selected configuration interaction (CI) calculations and second order perturbation theory are combined to systematically approach the full-CI limit. The resulting algorithm has negligible requirement for memory or disk space, being limited only by available cpu time. Comparison is made to existing full-CI benchmarks (DZ and DZP water, the oxygen atom and its anion, ammonia and the magnesium atom). In all cases the full-CI result is recovered to better than 0.1 kcal/mol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460537
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  • 7
    Electronic Resource
    Electronic Resource
    Ab initio molecular orbital study of the effects of basis set size on the calculated structure and acidity of hydroxyl groups in framework molecular sieves (1992)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 96 (1992), S. 10247-10257 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100204a029
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  • 8
    Electronic Resource
    Electronic Resource
    An ab initio investigation of disiloxane using extended basis sets and electron correlation (1992)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 96 (1992), S. 7958-7965 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100199a026
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  • 9
    Electronic Resource
    Electronic Resource
    Electron affinities of the first-row atoms revisited. Systematic basis sets and wave functions (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 6796-6806 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The calculation of accurate electron affinities (EAs) of atomic or molecular species is one of the most challenging tasks in quantum chemistry. We describe a reliable procedure for calculating the electron affinity of an atom and present results for hydrogen, boron, carbon, oxygen, and fluorine (hydrogen is included for completeness). This procedure involves the use of the recently proposed correlation-consistent basis sets augmented with functions to describe the more diffuse character of the atomic anion coupled with a straightforward, uniform expansion of the reference space for multireference singles and doubles configuration-interaction (MRSD-CI) calculations. Comparison with previous results and with corresponding full CI calculations are given. The most accurate EAs obtained from the MRSD-CI calculations are (with experimental values in parentheses) hydrogen 0.740 eV (0.754), boron 0.258 (0.277), carbon 1.245 (1.263), oxygen 1.384 (1.461), and fluorine 3.337 (3.401). The EAs obtained from the MR-SDCI calculations differ by less than 0.03 eV from those predicted by the full CI calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462569
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  • 10
    Electronic Resource
    Electronic Resource
    Isomers and excitation energies of C4 (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 3284-3290 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Coupled-cluster (CC) and many-body perturbation theory (MBPT) studies of the rhombic and linear structures of C4 are reported. For each isomer, the electronic spectra is obtained, and comparisons are made with experimental matrix-isolated ESR and electronic spectra. The closed-shell 1Ag rhombic ground state is found to be more stable than the 3∑−g state of the linear isomer by 5 kcal/mol at the highest level of calculation performed (CCSDT-1). However, the predicted spectrum for linear C4 is in reasonable agreement with the observed results. An allowed electronic transition for the rhombus is predicted to lie in the same region, suggesting the possibility that both isomers could coexist in the experiment. Finally, vibrational frequencies for the rhombic isomer are calculated using analytical second-order MBPT second derivatives to aid in the experimental identification of this transient species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450259
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