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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 116 (1994), S. 6925-6926 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 114 (1992), S. 9551-9559 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    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 102 (1995), S. 3703-3711 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The thermodynamic stabilities of the most stable even-membered and electrically neutral molecules (clusters) of phosphorus P2 through P18 are calculated in high accuracy. The larger clusters Pn, n(approximately-greater-than)4, turn out to be unstable at elevated temperatures, but are thermodynamically stable with respect to decay into P4 at low temperatures. To aid an experimental identification of such clusters, calculated vibrational frequencies, ionization potentials, and electronic excitation energies are supplied. As a side result we find the equilibrium bond length in P4 to be substantially shorter (below 220 pm) than the established experimental value r0=222.28±0.05 pm. © 1995 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 95 (1991), S. 8259-8265 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A generalization of Pitzer's equal contribution theorem is put forth. The new theorem specifies which types of matrix elements can be constructed using only symmetry-unique (batches of) integrals. A general and simple algorithm to use molecular point-group symmetry in electronic structure calculations is outlined.
    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 108 (1998), S. 8295-8301 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A scheme that fully exploits molecular point group symmetry in direct second-order many-body perturbation theory chemical shift calculations based on gauge-including atomic orbitals is presented and implemented. Representative calculations for the molecules B4(tBu)4 (Td symmetry) and [AlCp]4 (D2d symmetry) involving more than 600 basis functions demonstrate the applicability of the developed program to large symmetric molecules (which could be otherwise not treated) and indicate the importance of electron correlation effects for the reliable prediction of NMR chemical shifts in larger molecules. © 1998 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 96 (1992), S. 489-494 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We discuss how the computational obstacles related to energy denominators in various schemes for electron-correlation calculations can be circumvented by a Laplace transform technique. The method is applicable to a wide variety of electronic structure calculations. We discuss in detail an algorithm for the contribution of triple excitations in fourth-order Møller–Plesset perturbation theory, which grows only with the sixth power of the size of the system, as compared to conventional N7 algorithms. Special consideration is given to efficient schemes for numerical quadrature of the integrals occurring in the Laplace transformations.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 1262-1270 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a direct self-consistent-field (SCF)-type algorithm and its implementation for the computation of linear response properties: excitation energies, oscillator strengths, and frequency-dependent polarizabilities within the time-dependent SCF or random phase approximation. The treatment of singles configuration interaction for electronic excitations and Hartree–Fock instability criteria are covered as special cases. The algorithm is based on proven direct SCF methodology. This, together with full exploitation of molecular symmetry, opens the way to the treatment of large molecules. Applications to C60 strongly support the assignment of the lowest-lying dipole allowed transition to the strong band at 3.8 eV.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 97 (1993), S. 10964-10970 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 75 (1989), S. 1-10 
    ISSN: 1432-2234
    Keywords: Phosphanes ; Structure of phosphanes ; Ring strain ; Lone pair interactions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The molecules PH3, P2H4, P3H5, P3H3, P4H4, and P5H5 were treated at the SCF level using basis sets of DZP quality. Computed structure constants and energies indicate high stability for P5-ring systems and small ring strain for P3- and P4-ring systems. The computed values for the strain are 28 and 18 kJ/mol for P3H3 and P4H4, respectively. Neighbouring P atoms with transconfigured lone pairs are favoured in the monocyclic phosphanes considered in this work, as shown by the energy difference of about 10 kJ/mol between trans and cis configured lone pairs, and the shortening of P-P distances by about 2 pm for trans configured P atoms.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 87 (1993), S. 147-173 
    ISSN: 1432-2234
    Keywords: Correlation ; MP2 ; AO ; Laplace transform ; Bounds ; Parallel computer ; Gradient ; Crystal ; Solid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A novel formulation of MP2 theory is presented which starts from the Laplace transform MP2 ansatz, and subsequently moves from a molecular orbital (MO) representation to an atomic orbital (AO) representation. Consequently, the new formulation is denoted AO-MP2. As in traditional MP2 approaches electron repulsion integrals still need to be transformed. Strict bounds on the individual MP2 energy contribution of each intermediate four-index quantity allow to screen off numerically insignificant integrals with a single threshold parameter. Implicit in our formulation is a bound to two-particle density matrix elements. For small molecules the computational cost for AO-MP2 calculations is about a factor of 100 higher than for traditional MO-based approaches, but due to screening the computational effort in larger systems will only grow with the fourth power of the size of the system (or less) as is demonstrated both in theory and in application. MP2 calculations on (non-metallic) crystalline systems seem to be a feasible extension of the Laplace transform approach. In large molecules the AO-MP2 ansatz allows massively parallel MP2 calculations without input/output of four-index quantities provided that each processor has in-core memory for a limited number of two-index quantities. Energy gradient formulas for the AO-MP2 approach are derived.
    Type of Medium: Electronic Resource
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