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  • 1
    Electronic Resource
    Electronic Resource
    Ab initio spin-coupled description of the reactions CH2(1A1) + H2 .fwdarw. CH4 and CH4 .fwdarw. CH3(2A1') + H (1990)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 112 (1990), S. 5054-5060 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00169a009
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  • 2
    Electronic Resource
    Electronic Resource
    Study of the spectrum and decay of the doubly charged water ion using spin-coupled valence bond theory (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 1666-1676 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potential energy surfaces are computed for several low-lying singlet and triplet states of H2O++ using spin-coupled valence bond theory. Wide regions of the surfaces are investigated including all the dissociation processes to OH++H+ in different states, to O+H++H+ and to O++H++H. The correlation of all these states is very straightforward. The final wave functions are very compact (187 spatial configurations) and the electronic structure of the various states is interpreted directly in terms of the spin-coupled orbitals. This makes possible a completely new description of the ion–ion coincidence (PIPICO), Auger, and double charge transfer spectra of doubly ionized water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453230
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  • 3
    Electronic Resource
    Electronic Resource
    Electronic structure of diborane and octahydrotriborate(1-): boron-hydrogen-boron bridges and closed boron-boron-boron bonds (1991)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 95 (1991), S. 10617-10623 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100179a024
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  • 4
    Electronic Resource
    Electronic Resource
    New basis set superposition error free ab initio MO-VB interaction potential: Molecular-dynamics simulation of water at critical and supercritical conditions (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 3296-3303 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Recently, a controversy has come to light in literature regarding the structure of water in nonambient conditions. Disagreement is evident between the site–site pair correlation functions of water derived from neutron diffraction and those obtained by computer simulations which employ effective pairwise potentials to express the intermolecular interactions. In this paper the SCFMI method (self-consistent field for molecular interaction) followed by nonorthogonal CI (configuration interaction) calculations was used to determine a new water–water interaction potential, which is BSSE (basis set superposition error) free in an a priori fashion. Extensive calculations were performed on water dimer and trimer and a new parametrization of a NCC-like (Niesar–Corongiu–Clementi) potential was accomplished. This was employed in the molecular-dynamics simulation of water. The effect of temperature and density variations was examined. Acceptable agreement between site–site correlation functions derived from neutron diffraction data and from computer simulation was reached. In particular, a weakening of the hydrogen bonded structure was observed on approaching the critical point, which reproduces the experimental behavior. The simulations were performed using the MOTECC (modern techniques in computational chemistry) suite of programs. The present results show the importance of BSSE-free nonorthogonal orbitals in an accurate description of the intermolecular potential of water. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475726
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  • 5
    Electronic Resource
    Electronic Resource
    The nature of the carbon-carbon bond in the C2 and C2H2 molecules (1995)
    Springer
    Theoretical chemistry accounts 92 (1995), S. 49-59 
    Details
    ISSN: 1432-2234
    Keywords: Multiple bond ; Bent-bond ; Spin-coupled wavefunction ; Nonorthogonal spin-orbitals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The alternative description of the carbon-carbon bond in the C2 and C2H2 molecules in terms of σ/π or bent “banana” orbitals is analyzed here within the framework of the spin-coupled method. In particular, the first all-valence electron calculations on both models are presented. Comparison with previous work on these molecules demonstrates the importance of correlating all the valence electrons, especially for the C2 molecule which shows a change in relative stability of the two bond models when nonbonding electrons are correlated. The orbital picture provided by spin-coupled orbitals is presented together with a discussion on similarities and differences between the orbitals of C2 and C2H2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01134203
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  • 6
    Electronic Resource
    Electronic Resource
    Optimization of virtual orbitals in the framework of a multiconfiguration spin-coupled wave function (1998)
    Springer
    Theoretical chemistry accounts 99 (1998), S. 8-17 
    Details
    ISSN: 1432-2234
    Keywords: Key words: Spin-coupled valence bond ; Orbital optimization ; Multiconfiguration ; Virtuals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. A new method is introduced for the optimization of nonorthogonal virtual orbitals for use in general multiconfiguration spin-coupled wave functions. The use of a number of highly effective approximations greatly reduces the computational effort involved, the most important being the use of a second-order perturbation expression for the energy and an approximate expression for the elements of the Hessian. As a result, the overall scheme scales very favourably with respect to the numbers of active electrons and of basis functions, making it suitable for the accurate study of large systems. Benchmark calculations are presented for the dissociation of LiH(X1Σ+) and Li2(X1Σ+ g ) using a highly compact four-configuration wave function. Standard spin-coupled valence bond expansions in the same virtual space are required to be significantly larger before equivalent results are obtained. The results are shown to compare very favourably with full valence complete active space self-consistent field calculations using an identical basis, and binding energies are within 4% of the values obtained from full configuration interaction calculations in the same basis set.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002140050297
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  • 7
    Electronic Resource
    Electronic Resource
    Expansion of the spin-coupled wavefunction in Slater determinants (1993)
    Springer
    Theoretical chemistry accounts 85 (1993), S. 261-270 
    Details
    ISSN: 1432-2234
    Keywords: Spin-coupled wavefunction ; Slater determinants ; Nonorthogonal spin-orbitals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The expansion of the spin-coupled wavefunction in Slater determinants constructed from nonorthogonal spin-orbitals is discussed. It proves possible to generate from cofactors of the appropriate overlap matrix all the density matrices, up to fourth order, required for the variational optimization of the wavefunction. The computational effort inherent in this ‘super-cofactor’ strategy scales in a very acceptable manner with the number of electrons.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01129116
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  • 8
    Electronic Resource
    Electronic Resource
    An orthogonal approach to determine extremely localised molecular orbitals (2000)
    Springer
    Theoretical chemistry accounts 103 (2000), S. 417-422 
    Details
    ISSN: 1432-2234
    Keywords: Key words: Localised molecular orbitals – Nonorthogonal orbitals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract. The introduction of extremely localised molecular orbitals, a current issue in modern physical chemistry, justifies chemical intuition and provides a useful tool towards the description of large molecules. In this paper, a possible strategy to determine these orbitals is proposed. The algorithm implemented has been tested by effecting computations on water, ammonia, benzene and naphthalene by employing different intramolecular partitionings. Ethane and biphenyl have been considered for application of the algorithm to the study of rotational barriers. Our scheme also includes the possibility to compute derivatives with respect to nuclear coordinates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002149900073
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  • 9
    Electronic Resource
    Electronic Resource
    The nature of the carbon–carbon bond in the C2 and C2H2 molecules (1995)
    Springer
    Theoretica chimica acta 92 (1995), S. 49-59 
    Details
    ISSN: 0040-5744
    Keywords: Key words: Multiple bond ; Bent-bond ; Spin-coupled wavefunction ; Non-orthogonal spin ; orbitals
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary.  The alternative description of the carbon–carbon bond in the C2 and C2H2 molecules in terms of σ/π or bent “banana” orbitals is analyzed here within the framework of the spin-coupled method. In particular, the first all-valence electron calculations on both models are presented. Comparison with previous work on these molecules demonstrates the importance of correlating all the valence electrons, especially for the C2 molecule which shows a change in relative stability of the two bond models when nonbonding electrons are correlated. The orbital picture provided by spin-coupled orbitals is presented together with a discussion on similarities and differences between the orbitals of C2 and C2H2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01134203
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    Paper (German National Licenses)
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  • 10
    Electronic Resource
    Electronic Resource
    Modern valence-bond description of the electronic structure of benzocyclobutadiene (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 60 (1996), S. 545-552 
    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: The ground state of benzocyclobutadiene, a bicyclic molecule with 8π electrons containing a benzene and a cyclobutadiene ring, is studied by means of modern valence bond (VB) theory in its spin-coupled (SC) form and the complete-active-space self-consistent field (CAS SCF) approach. The CAS SCF wave function is used to optimize the geometry, and SC theory - to obtain a well-correlated and easy to visualize and understand model of the active space hosting the π electrons. It is shown that the π system of the ground state of benzocyclobutadiene can be described with sufficient accuracy as a combination of the π systems of a distorted benzene ring and an isolated double bond. Each of the eight SC orbitals is found to be well-localized about one carbon atom only, with small distortions toward its nearest neighbors. The analysis of the optimal active-space spin-coupling pattern within the SC wave function for benzocyclobutadiene shows unambiguously that this molecule inherits neither the aromatic nor the antiaromatic character of its cyclic components, and it is most appropriate to regard it as nonaromatic. © 1996 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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