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  • American Institute of Physics (AIP)  (4)
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  • 1
    Electronic Resource
    Electronic Resource
    Size-consistent self-consistent truncated or selected configuration interaction (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 1240-1254 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Based on the principle of intermediate effective Hamiltonians, a simple procedure is proposed in order to eliminate the unlinked contributions of any truncated or selected configuration interaction (CI). The corrections are diagonal energy shifts, easily calculated. A self-consistent version is proposed, which insures separability if localized molecular orbitals (MO) are used. In the special case of double CI, the present method is an improved version of the coupled electron pair approximation (CEPA), but it may be applied to any selected model space, involving configurations of various degrees of excitation. The efficiency of the proposed algorithms is illustrated on a series of test calculations performed on Be2, F2, N2, and NH3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465368
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  • 2
    Electronic Resource
    Electronic Resource
    Multireference self-consistent size-consistent singles and doubles configuration interaction for ground and excited states (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 8908-8921 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: One proposes a state-specific self-consistent dressing of the configuration interaction (CI) matrix built on a multireference space and all the singly and doubly substituted determinants. The dressing insures size consistency [and separability when localized molecular orbitals (MOs) are used]. In the here-proposed solution, which generalizes a previous single reference method [(SC)2CI, J. Chem. Phys. 99, 1240 (1993)] valid only for the research of the ground state, all the reference determinants play an equal role and the method is applicable to excited states. The implementation will be simpler if the reference space is a complete active space, but this restriction is not compulsory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468083
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  • 3
    Electronic Resource
    Electronic Resource
    Many-body perturbation calculation on Be using a multiconfiguration model space and an intermediate Hamiltonian (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 1046-1052 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a perturbation calculation of the ground state energy of the Be atom starting from a multiconfigurational model space and using the new concept of an intermediate Hamiltonian. The traditional MC-MBPT is known to diverge for this problem, whereas our method strongly converges. This convergence is explained by the fact that this method is free from any intruder state problem. The second-order calculation yields 140% of the correlation energy with a single reference model space, 93% with a multireference, and 98% with our method demonstrating the efficiency of the intermediate Hamiltonian.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454273
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  • 4
    Electronic Resource
    Electronic Resource
    Direct theoretical ab initio calculations in exchange coupled copper(II) dimers: Influence of the choice of the atomic basis set on the singlet–triplet splitting in modeled and real copper dimers (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 5048-5052 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The singlet–triplet splitting (2J=EST) is calculated in bis-[bromo-(N,N-diethylaminoethanolato)copper(II)], belonging to the group of alkoxo-bridged copper(II) dimers, by a recently proposed ab initio method. The singlet–triplet splitting energy is obtained by a perturbation expansion closely related to Anderson's formalism. The role of all valence electrons is taken into account and it is shown to be very important in order to obtain a satisfying agreement with the experimental result. Two important facts, from a computational point of view, are tested: influence of the atomic basis set size, and influence of modifying of the ligands. Changes in the basis set of the bridging atoms can induce variations in the results from 10% to 20%. As a final result, the theoretical value of the real complex is calculated to 2J(calc)=−1095 cm−1 and agrees with the experimental one 2J(exp)=−817 cm−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448626
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