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  • 1
    Electronic Resource
    Electronic Resource
    On the potential energy surface for collinear OH+2 (4Σ−) (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 3774-3777 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The potential energy surface for collinear OH+2 (4Σ−) has been investigated at the configuration interaction (CI) level using large primitive basis sets of Gaussian type orbitals (GTO) and the general atomic natural contraction (ANO). The CI calculations were carried out using the CIPSI algorithm and the accuracy established by comparison with full CI (FCI) test calibrations on the atoms and molecules of interest in the present work. For the reaction O+(4Su)+H2(1Σ+g)→OH+(3Σ−)+H(2Sg) the calculated value for the energy change of the reaction (ΔE) is −0.30 eV to be compared with an experimental value of −0.45 eV. The error in ΔE arises from the error in the ionization potential of oxygen and does only affect the reactants but not the products, while the discrepancy with the experiment is limited by the finite size of the basis set and not by truncations on the CI expansion. The collinear OH+2 minimum has been found to lie 0.338 eV below the products with an estimated accuracy of 0.01 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459749
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  • 2
    Electronic Resource
    Electronic Resource
    Theoretical analysis of bonding in monomeric and polymeric C5H5M compounds (1984)
    s.l. : American Chemical Society
    Organometallics 3 (1984), S. 759-764 
    Details
    ISSN: 1520-6041
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/om00083a020
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  • 3
    Electronic Resource
    Electronic Resource
    Ab initio electronic structure of PtH+, PtH, Pt2, and Pt2H from a one-electron pseudopotential approach (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 8500-8506 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A one-electron pseudopotential having an averaged d9 open shell in the core has been obtained for the ground state of Pt atom. With this pseudopotential we have studied the electronic structure of PtH+, PtH, Pt2, and Pt2H using large basis sets and an exact full configuration interaction wave function. In order to obtain reliable results, core–core repulsion, core–polarization and core–valence correlation effects have to be taken into account. These effects have been included through suitable core–core and core–polarization potentials. Comparison between existent and present calculations show that the one electron pseudopotential for Pt can be regarded as an average of the different real states arising from coupling of s valence shells with the open 5d9 levels of the d shell. Provided the extreme simplicity of the model, results obtained for small platinum containing systems are in fair agreement with previous highly sophisticated calculations and indicate that this one-electron pseudopotential for Pt can be effectively used to model surroundings of large surface cluster models or Pt complexes where d–d bonding is not dominant. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471600
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  • 4
    Electronic Resource
    Electronic Resource
    Direct determination of localized Hartree–Fock orbitals as a step toward N scaling procedures (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 10044-10050 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method is proposed for the solution of the self-consistent field equations that can lead to localized occupied and virtual molecular orbitals, avoiding the need for solving for the canonical molecular orbitals. The method starts with strongly localized "guess molecular orbitals", it is nonperturbative and proceeds through the diagonalization of single configuration interaction matrices which may be rendered size-consistent through appropriate coupled electron pair approximation or coupled-cluster-type dressings. We see a potential utility for the method in applications to large systems where localized orbitals will improve the scaling of the computational resources required with increasing system size. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474161
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  • 5
    Electronic Resource
    Electronic Resource
    The importance of correlation effects on the bonding of atomic oxygen on Pt(111) (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 7192-7199 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The adsorption properties and the bonding nature of atomic oxygen adsorbed on the three-hollow sites of Pt9 and Pt25 cluster models of the Pt(111) surface have been studied by means of ab initio wave functions. Correlation effects have been introduced by various methods: single and multireference second-order perturbation theory, multireference configuration interaction, and density functional corrections to the Hartree–Fock energy using a variety of expressions of density functionals. While the adsorption and vibrational properties of adsorbed oxygen are sufficiently well described at the Hartree–Fock level, the adsorption energy is completely wrong as the system is unbound in the one-electron approximation while it is strongly bound at the correlated level. The use of correlation functional based on the Hartree–Fock density is not sufficient to obtain a correct estimate of the strength of the bond. We will also show that the bonding of oxygen to Pt has a partial ionic character and the effect of correlation is to enhance the importance of covalent contributions to the bonding. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472522
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  • 6
    Electronic Resource
    Electronic Resource
    An efficient improvement of the string-based direct selected CI algorithm (1995)
    Springer
    Theoretical chemistry accounts 92 (1995), S. 305-313 
    Details
    ISSN: 1432-2234
    Keywords: Discius algorithm ; Configuration interaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary A modified version of the Direct Selected Configuration Interaction Using Strings (DISCIUS) code is presented. From a series of test calculations it is shown that the string-based direct-CI algorithm is also very efficient in larger examples than the ones we showed in our former version. The performance of this new code with respect to the computer time is reasonable as well as its storage requirements. Hence, we present a new tool able to treat more than 106 determinants of a variational space that does not have a defined structure, i.e. a selected or any way truncated CI.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01113870
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  • 7
    Electronic Resource
    Electronic Resource
    Another way to implement the Powell formula for updating Hessian matrices related to transition structures (1999)
    Springer
    Journal of mathematical chemistry 25 (1999), S. 85-92 
    Details
    ISSN: 1572-8897
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mathematics
    Notes: Abstract A way to update the Hessian matrix according to the Powell formula is given. With this formula one does not need to store the full Hessian matrix at any iteration. A method to find transition structures, which is a combination of the quasi‐Newton–Raphson augmented Hessian algorithm with the proposed Powell update scheme, is also given. The diagonalization of the augmented Hessian matrix is carried out by Lanczos‐like methods. In this way, during all the optimization process, one avoids to store full matrices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019168013391
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  • 8
    Electronic Resource
    Electronic Resource
    Using full-CI algorithms in Bethe-Goldstone-type expansions of the correlation energy (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 35-43 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the early 1960s, Nesbet proposed to develop correlation energy in terms of two-, three-, four-, etc., electron contributions. This expansion was, in principle, applicable to a large number of electrons without a size-extensivity error. The now available full-CI algorithms may be used to obtain those expansions in terms of either occupied spin - orbitals or, more efficiently, in terms of sets of occupied or virtual molecular orbitals. Tests on the NH3 molecule with a DZP basis-set problem show the slow convergence of this approach. © 1997 John Wiley & Sons, Inc.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Analysis of the convergence of the general coupling operator method for one-configuration-type wave functions (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Computational Chemistry 19 (1998), S. 368-376 
    Details
    ISSN: 0192-8651
    Keywords: general coupling operator ; coupling operator ; wave functions ; Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Computer Science
    Notes: We comment on the convergence of the general coupling operator for all types of one-configuration or multiconfigurational wave functions that still preserve the one-configuration structure for the energy expression. The choice on the best arbitrary real and antisymmetric parameters inherent in the coupling operator methodology is discussed, giving a theoretical reason. Another type of coupling operator is defined, presented, and analyzed. Finally, we give some numerical examples related to the low-lying electronic states of a cluster model for K2NiF4 solid.   © 1998 John Wiley & Sons, Inc.   J Comput Chem 19: 368-376, 1998
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
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