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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 44 (1977), S. 1-7 
    ISSN: 1432-2234
    Keywords: Correlation energy ; Ethylene, V-N transition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The V-N vertical transition of planar ethylene has been investigated by means of a large Gaussian basis set, taking into account both the SCF and correlation energies. It is shown that in this case the SCF function, which would lead to a valuation of the Rydberg character at around 80%, does not provide an adequate description of the V state. The correlative effects bring about a lowering of the percentage of the Rydberg character to 38%. The calculated value for the transition energy is in excellent accord with the experimental data.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 53 (1979), S. 377-381 
    ISSN: 1432-2234
    Keywords: C2H 6 + ion ; relative stability of the2 A 1g and2 E g states of ∼
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Anab initio study of the relative stability for the states2 A 1g and2 E g of C2H 6 + has been carried out. The results of the Open Shell Restricted Hartree-Fock calculations lead to assign the2 A 1 g as the ground state of the molecule in agreement with previous SCF calculations. The correlation energy associated to both states has been calculated within the correlation hole model and the results, contrary to those obtained from Configuration Interaction calculations, do not alter qualitatively the conclusions from SCF.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 47 (1978), S. 305-314 
    ISSN: 1432-2234
    Keywords: Open-shell theory ; RHF equations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract We have derived the expressions for the extremum condition of 〈E〉, corresponding to any wave function. These expressions are given as a function of the spin orbitals. We have carried out the derivation considering the spin orbitals as vectors belonging to an orthonormal basis. The corresponding variational equations have been derived introducing the condition that the norm of the wave function is constant, as the only additional constraint. From the expression obtained for the first variation of the matrix elements of H, as a function of the spin orbitals, we have derived the RHF equations for a simple case. In the present procedure, the couplings between orbitals of different shells appear directly, being defined explicitly, and they may be taken as corresponding with the elements of a Hermitian matrix. The calculations that we have carried out show that the coupling operators defined in the paper give results which are variationally correct.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 54 (1979), S. 53-58 
    ISSN: 1432-2234
    Keywords: Ethane ionization spectrum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This work is an extension of a previous study on the assignment of the peaks of the photoionization spectrum of C2H6 [1]. The model of the correlation hole is reconsidered in order to carry out a new study of the states2 A 1g ,2 E g ,2 E u and2 A 2u of the C2H 6 + The qualitative relations which the average mass of the electrons in the Coulomb hole must have for the four states of the C2H 6 + , lead to a new criterion for the assignation of the peaks of the spectrum. The arrangement obtained for the two lower peaks is in agreement with those obtained previously [1].
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 77 (1990), S. 207-212 
    ISSN: 1432-2234
    Keywords: Correlation energy ; Functional density ; Correlation factor ; Ionization energies ; Electron affinities
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The correlation energy of two- and four-isoelectronic series, a representative example for which the existing spin-density functionals fails, is calculated using the Colle and Salvetti method, considering mono- and multideterminantal wave functions. The results are in agreement with experimental data, and show the potentiality of this method when it is applied to wave functions including the most relevant configurational features. Also, results for the ionization energies and electron affinities of first- and second-row atoms are reported.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 54 (1979), S. 53-58 
    ISSN: 1432-2234
    Keywords: Ethane ionization spectrum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract This work is an extension of a previous study on the assignment of the peaks of the photoionization spectrum of C2H6 [1]. The model of the correlation hole is reconsidered in order to carry out a new study of the states2 A 1g ,2 E g ,2 E u and2 A 2u of the C2H 6 + The qualitative relations which the average mass of the electrons in the Coulomb hole must have for the four states of the C2H 6 + , lead to a new criterion for the assignation of the peaks of the spectrum. The arrangement obtained for the two lower peaks is in agreement with those obtained previously [1].
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 70 (1986), S. 297-302 
    ISSN: 1432-2234
    Keywords: Li-CO2 complex ; UHF plus correlation calculations ; Potential energy surfaces
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Unrestricted Hartree-Fock calculations with large basis sets, including d-functions, and the estimation of the correlation energy, show that the potential energy surface for the Li-CO2 complex is built from the crossing of two states, each of them corresponding to a different electron arrangement. One has a strong ionic character and the other is of van der Waals type. Each portion of the energy surface presents a minimum, which is stable in respect to the dissociation limit.
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 2022-2026 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The prevailing approach in density-functional theory makes use of universal functionals, valid for any number of electrons (N). In this article and following the work of Lieb [E. H. Lieb, Int. J. Quantum Chem. 24, 243 (1983)], we argue that the use of N-dependent functionals could be an equally valid approach. Size consistency (dissociation into proper fragments) puts restrictions on the form that N-dependent functionals may adopt. We propose a simple procedure for correcting the size-consistency problem of existing N-dependent functionals that also provides an original way of designing new ones. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    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 comparative dynamical analysis of several quasi-exact wavefunctions for helium has been carried out by computing their corresponding correlation coefficients. The aim is to use the resulting information to study the correlation included in approximate wavefunctions within the factor correlation model. Information about the possibility of making simplifications in the approximate wavefunctions and about the flexibility of the quasi-exact wavefunctions is also obtained.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    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: Calculations have been made at the minima of the X1A1 ground state of the ozone molecule. The equilibrium geometries have been obtained by means of CID calculations. The criterion adopted for the choice of configurations gives realistic results. CIPSI calculations at the two minima lead to an estimated gap of 0.92 eV between them.Our results agree with the analysis of previous theoretical works on the relative stability of open and cyclic zone structures, showing that the D3h minimum is stable relative to the ground state dissociation limit.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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