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  • 1
    Electronic Resource
    Electronic Resource
    Atomic and molecular correlation energies with explicitly correlated Gaussian geminals. V. Cartesian Gaussian geminals and the neon atom (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 3964-3974 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Correlation energy through third order and various coupled-pair correlation energies have been calculated for the neon atom using a basis set of explicitly correlated Gaussian geminals. Improved versions of functionals introduced in earlier papers of this series have been used. Our results are in very good agreement with accurate results of Lindgren and Salomonson and Jankowski et al. obtained with techniques specific for atoms. Our values are estimated to be accurate to about 1 mhartree. The results of this paper show that the method of Gaussian geminals is very competitive for systems with p electrons and should be able to achieve "chemical accuracy'' for small molecules containing first and second row atoms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450918
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  • 2
    Electronic Resource
    Electronic Resource
    Monte Carlo eigenvalue and variance estimates from several functional optimizations (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 6622-6633 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using several simple systems as examples, we show that the choice of optimization functional can have a significant influence on the accuracy of variational Monte Carlo calculations. In addition, we demonstrate that the Monte Carlo analog of the Rayleigh–Ritz procedure, which explicitly orthogonalizes ground and excited states, can be used to produce accurate eigenvalue and variance estimates of excited states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461532
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  • 3
    Electronic Resource
    Electronic Resource
    New Born–Oppenheimer potential energy curve and vibrational energies for the electronic ground state of the hydrogen molecule (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 3278-3283 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Born–Oppenheimer potential energy curve for the electronic ground state of the hydrogen molecule has been computed for internuclear distances 0.2≤R≤12.0 bohr. At all R the energies are lower than any previously reported values. At the equilibrium distance the improvement is negligible; its largest value, 0.47 cm−1, has been obtained for R=2.4 bohr. Vibrational energies have been computed for all isotopic species using the new potential energy curve. For H2, HD, and D2 the recent nonadiabatic corrections of Wolniewicz have been included. The resulting dissociation energies of H2 and HD agree with the experimental values within the experimental error limits; for D2 the discrepancy amounts to 0.6±0.3 cm−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450258
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  • 4
    Electronic Resource
    Electronic Resource
    Fock-space coupled-cluster method (1991)
    Springer
    Theoretical chemistry accounts 80 (1991), S. 483-507 
    Details
    ISSN: 1432-2234
    Keywords: Coupled-cluster method ; Fock-space formalism ; PPP model ; Electronic spectra calculations ; Intruder states
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A generalization of the single-reference coupled-cluster method, employing the algebraic properties of the fermionic Fock space, is presented. This Fock-space coupled-cluster (FSCC) method is capable of providing not only the ground-state energy of anN-electron system, but also an important fraction of system's excitation spectrum, including ionization potentials, electron affinities, and excitation energies corresponding toN-electron singlet and triplet states. The FSCC method is applied to study the electronic spectra corresponding to the Pariser-Parr-Pople model of butadiene, hexatriene, and benzene, with the full configuration-interaction results taken as the reference. The problem of intruder states is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01119667
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  • 5
    Electronic Resource
    Electronic Resource
    Coupled-cluster method with optimized reference state (1984)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 26 (1984), S. 267-291 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We propose a variant of the coupled-cluster (CC) method in which spin orbitals of the reference Slater determinant are optimized in a self-consistent way. This approach is a reformulation of the Brueckner-Hartree-Fock (BHF) method used in nuclear physics and known also as the exact SCF method. We discuss the use of the reference-state determinants built of HF, natural, and Brueckner spin orbitals, with relations among them investigated in terms of the many-body perturbation theory (MBPT). It is shown that the Brueckner spin orbitals emerge as a convenient basis set in the coupled-cluster method and equations that determine these spin orbitals are found. The Brueckner spin orbitals can be calculated as eigenvectors of a certain Hermitian one-electron operator which has a form of the Hartree-Fock operator plus a “correlation potential” depending linearly on two- and three- electron cluster amplitudes. The usual decoupling scheme in the coupled-cluster method leads to a hierarchy of approximations; in the first nontrivial one the three-electron cluster amplitudes are neglected, and the two-electron ones are determined by solving Čižek's CPMET equations. We also analyze the problem of spatial, spin, and time-reversal symmertry in the CC and BHF methods. If (and only if) the reference-state determinant belongs to a one-dimensional representation of a certain symmetry subgroup of the system, the CC operator and the BHF one-electron operator are invariant with respect to this subgroup. Thus the restricted (entirely symmetry-adapted) version of the BHF method can be formulated only for the closed-shell systems. This is done for the above-mentioned approximate BHF method. We discuss also the usefulness of the BHF method in application to extended metallic systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560260827
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  • 6
    Electronic Resource
    Electronic Resource
    Slater orbital molecular integrals with numerical fourier transform methods.Supported in part by the National Science Foundation (Grant GP-31373X). Also supported by the Air Force Office of Scientific Research, Office of Aerospace Research, USAF, under Grant No. AFOSR-71-1992. The United States Government is authorized to reproduce and distribute reprints for governmental purposes notwithstanding any copyright notation hereon. I. (coplanar) multicenter exchange integrals over 1s orbitals (1973)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 7 (1973), S. 233-251 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Slater orbital r12-1 integrals are calculated with a numerical Fourier-transform method based on a formulation first given by Bonham, Peacher and Cox. Spherical wave expansions are introduced that decouple the Feynman integrations for the charge distribution Fourier transforms. The Feynman integrals are evaluated semianalytically, and their properties are analyzed in detail. The final computational step involves a numerical integration over charge distribution quantities. Results for (coplanar) multicenter exchange integrals over 1s orbitals are given. As long as the charge distributions are overlapping considerably, the method gives good results, even when these distributions are highly asymmetric. The method as presently implemented fails when highly disconnected charge distributions are involved.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560070209
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  • 7
    Electronic Resource
    Electronic Resource
    Symmetric and symmetry-broken Hartree-Fock solutions of one-dimensional models (1989)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 36 (1989), S. 659-667 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pariser-Parr-Pople Hartree-Fock crystal orbital calculations (both restricted and unrestricted versions) are performed for one-dimensional models of π-electron polymers. The π-electron band structures corresponding to symmetric and nonsymmetric solutions have been calculated. To investigate the influence of the form of the interelectronic interaction, the calculations were performed with the Mataga-Nishimoto (MN) formula and a modified Mataga-Nishimoto (MMN) formula for two-electron integrals. We have found that curves of the points of the minimum total energy per unit cell for the alternating models are very similar, but band structures and energy gaps are quite different when the MN formula was substituted with the MMN formula for two-electron integrals.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560360510
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  • 8
    Electronic Resource
    Electronic Resource
    On the removal of the exchange singularity in extended systems (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 81-89 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A serious problem in the ab-initio Hartree-Fock calculation for extended systems is a singularity in the exchange contribution to the band energies (the “exchange pathology”). In the homogeneous electron gas this pathology is exactly cancelled by the correlation contribution arising from the sum of all time-ordered ring diagrams (RPA approximation). In this article we show that this cancellation is more general and does also occur in periodically extended systems. © 1993 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480811
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  • 9
    Electronic Resource
    Electronic Resource
    Rules for intrinsically (super) conducting polymers (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 48 (1993), S. 245-248 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We propose a number of rules based on topological and structural considerations for the synthesis of intrinsically conducting polymeric materials. These rules can be summarized as follows: (i) The polymer has to have a glide plane or a twofold screw axis when infinitely extended; (ii) the unit cell must contain 4N + 2 valence electrons; (iii) the packing into the solid is restricted by symmetry rules that conserve the twofold degeneracy caused by rule (i). These rules are necessary (but not sufficient) for superconductivity. The inorganic polymer poly(sulfur-nitride), which is a metallic superconductor with a critical temperature of Tc = 0.33 K, is identified as a striking example of these rules. © 1993 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560480826
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  • 10
    Electronic Resource
    Electronic Resource
    Electronic-structure studies of solides. V. Rigorous Hartree-Fock treatment of metallic hydrogen using a plane-wave basisThe United States Government is authorized to reproduce and distribute reprints for governmental purposes notwithstanding any copyright notation hereon (1977)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 12 (1977), S. 145-160 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We have performed Hartree-Fock calculations for simple cubic metallic hydrogen crystals using Bloch functions expanded in plane waves, All integrals were evaluated accurately including exchangeterms. Increasingly larger basis sets were used, and the total Hartree-Fock energy obtained with the maximum number of plane waves (27) was -0.4770 hartrees/atom. This total energy is believed to be within a few millihartress of the Hartree-Fock limit results. The deficiency of a plane-wave expansion to represent the atomic cusps, however, makes it difficult to obtain the exact Hartree-Fock limit with a plane-wave expansion. When the correlation energy (calculated in the random-phase approximation with Hartree-Fock bands and functions as zeroth order states) is added, and upper limit of -0.501 hartrees/atom is found for the total energy of this system. The Fermi surface was found to touch the Brillouin zone boundaries around the X points due to an appreciable depression of the band energies in that part of the Brillouin zone. The equilibrium lattice spacing (a = 2.705 bohrs) was slightly smaller than that obtained earlier with an atomic orbital basis.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560120113
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