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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2869-2880 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A molecular system is partitioned into fragments. Within the context of extended geminal models, it is shown that the total electronic energy can be written as a sum of intra- and interfragment energies. On the basis of this type of analysis, the difference in equilibrium bond angles in H2O and H2S, NH3 and PH3, is discussed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 262-273 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model aimed at describing intermolecular interactions is formulated within the context of extended geminal models. The model has the following properties: It has a conceptual structure which facilitates interpretation. The model can be applied for any intersystem distances. The model is size extensive. Basis set superposition errors can be practically eliminated. The model is computationally efficient. A test calculation on the helium dimer yields a well depth of 10.64 K. The experimental determined value of the well depth is (10.79±0.22) K.
    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 99 (1993), S. 277-285 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A set of computational models, denoted extended group function models, are introduced for describing intermolecular interactions of closed shell systems. The models have the following properties: They have a conceptual structure which facilitates interpretation. The models can be applied for any intersystem distances. The models are size extensive. The basis set superposition error can be eliminated at the correlation level. The models are computationally efficient. A test calculation is performed on the complex Ne⋅Li+.
    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 89 (1988), S. 441-445 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Within the framework of the general extended geminal models, two new approximate models are introduced. Compared with previous models, the double pair correction terms {εKL} are given a more accurate representation. The models are tested against full CI calculations on the beryllium atom, the neon atom, and the beryllium dimer.
    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 102 (1995), S. 7088-7094 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new computational method within the framework of extended group function models is introduced for describing intermolecular interactions between closed shell systems. The model is size extensive, applicable for any intersystem distance, and has a conceptual structure which facilitates interpretation. The basis set superposition error can be eliminated at the correlation level. Test calculations have been performed on the helium dimer and the helium trimer. © 1995 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 102 (1995), S. 7095-7105 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An extended group function model has been applied to determine the three-body potential for the ground state of the helium trimer. The basis set for the calculations is an uncontracted (17s,6p,4d,3f) set of Gaussian type functions contracted to [8s,6p,4d,3f]. Three different types of configurations were considered: (i) equilateral triangles of side R, R∈{3.5,4.0,...,8.5,9.0} a.u., (ii) linear configurations with R12=R23, R12∈{3.5,4.0,...,8.5,9.0} a.u., and (iii) a set of pseudo-random configurations. For the equilateral triangular configurations and the linear configurations, and with equal distances larger than 5.5 a.u., the magnitude of the ratio between the three-body potential and the sum of the corresponding two-body potentials, is less than 0.003. The value of the three-body potential for the triangular and the linear configuration with equal distance R=5.669 289 a.u.=3 A(ring), is respectively 0.040 μH and −0.045 μH. In the long range region the calculated three-body potential is very close to the Axilrod–Teller triple-dipole energy. © 1995 American Institute of Physics.
    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 105 (1996), S. 2751-2761 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Within this framework of extended geminal models, new and improved approximations are introduced for the calculation of electron triple pair correlation terms. There are three levels of increasing accuracy for these terms based on the coupled-cluster models: a model of single and double excitations, a model correct up to fourth order, and a model correct up to fifth order CCSD(TQ). A test calculation on the neon atom demonstrates that by adopting the CCSD(TQ) model for the triple pair correlation terms, the extended geminal model recovers 99.88% of the full CI valence shell correlation energy. To reduce the computational work involved in calculating double pair correlation terms and triple pair correlation terms, a modified set of natural orbital (NOs) is introduced. On the basis of these NOs a truncated virtual orbital space is defined. Test calculations on the neon atom, the helium dimer, and the helium trimer demonstrate that the dimension of this truncated space can be chosen to be considerably smaller than the dimension of the full virtual space at a small sacrifice in accuracy. The additive structure of the correlation terms implies that the models are appropriate for implementation on parallel processor computers. The extended geminal models have properties which make them ideally suited for describing intermolecular interactions: the models have a conceptual structure which facilitates interpretation, they can be applied for any intersystem distances, the models are size-extensive, they generate no basis set artifacts (basis set superposition errors), and the models are reliable and accurate. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 114 (1992), S. 511-516 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Chemical Physics 174 (1993), S. 345-350 
    ISSN: 0301-0104
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Chemical Physics 167 (1992), S. 263-275 
    ISSN: 0301-0104
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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