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1.
Fabio E. Penotti 《International journal of quantum chemistry》2006,106(5):1153-1159
Nonorthogonal single‐configuration and multiconfiguration ab initio calculations are carried out on the BeH2 molecule in its equilibrium (D∞h) geometry, using a highly optimized even‐tempered Slater‐type orbital (STO) basis set. The results are used as a basis for a discussion of the electronic structure of the molecule in modern‐VB terms. A value of Re = 1.329 Å is obtained. Values are also obtained for the symmetric‐stretch harmonic frequency (2053 cm?1), electric quadrupole moment (?5.60 Buckingham), and nuclear quadrupole coupling constants (?3.59 MHz for 9Be and 0.0915 MHz for 2H). © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献
2.
Menéndez FE Espina Aránzazu Trobajo Camino García José R. Rodríguez Julio 《Journal of inclusion phenomena and macrocyclic chemistry》1993,15(3):215-230
Journal of Inclusion Phenomena and Macrocyclic Chemistry - The intercalation reactions betweenn-alkylamines and α-titanium phosphate in aqueous media have been investigated. The compounds with... 相似文献
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Fabio E. Penotti 《International journal of quantum chemistry》2000,78(1):24-31
The implications of orbital symmetry for a configuration's spin function are considered from the fairly general viewpoint required for multiconfiguration wave functions employing nonorthogonal orbitals. A general procedure is derived for the imposition of the spin constraints that may be necessary to ensure a given configuration, or a set of configurations as a whole, exhibit required symmetry properties, thus preventing symmetry contamination of the overall electronic wave function. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 24–31, 2000 相似文献
5.
Fabio E. Penotti David L. Cooper Peter B. Karadakov Robert Ponec 《International journal of quantum chemistry》2020,120(11):e26183
Motivated by the particularly short metal-metal distance that has been predicted for the D3h [BeH3Be]+ cation, comparable to those anticipated for triple bonds, we investigate the nature of the bonding interactions in the D3h [MH3M]+ cations (M = Be, Mg). CCSD(T)/cc-pVQZ calculations are used to determine optimized geometries for all of the various species, including those “capped” by He or Ne atoms (as proxies for an inert gas matrix). The primary tools that are then used to investigate the nature of the chemical bonding are spin-coupled generalized valence bond calculations and the analysis of localized natural orbitals and of domain-averaged Fermi holes. The various results for all of the systems considered indicate the presence of highly polar three-center two-electron M─H─M bonding character instead of any significant direct metal-metal bonding. 相似文献
6.
Fabio E. Penotti 《International journal of quantum chemistry》1993,46(4):535-576
An ab initio method for the calculation of atomic and molecular electronic wave functions is presented. The “Optimized-Basis-Set Multiconfiguration Spin-Coupled” (OBS –MCSC ) method may be viewed either as a multiconfiguration generalization of the spin-coupled approach or as a nonorthogonal variant of the MCSCF method. In addition, the OBS –MCSC method optimizes the basis-set exponential parameters simultaneously with all other variational parameters, through a second-derivative minimization procedure. Explicit analytic expressions for the required first and second derivatives of the energy with respect to all variational parameters are obtained. Test calculations prove the capability of the method to yield compact yet accurate electronic wave functions.© 1993 John Wiley & Sons, Inc. 相似文献
7.
Penotti FE 《Journal of computational chemistry》2006,27(6):762-772
A new procedure is presented for introducing arbitrary orbital-orthogonality constraints in the variational optimization of otherwise nonorthogonal multiconfiguration electronic wave functions. It is based on suitable analytical changes to the expressions for the first and second derivatives of the electronic energy with respect to the independent variational parameters, and can be applied in the presence of symmetry constraints. It is tested using a second-derivative optimization procedure, the Optimized Basis Set -- Generalized Multiconfiguration Spin-Coupled (OBS-GMCSC) approach, that can treat basis-function exponential parameters as variational parameters, to be optimized simultaneously with configuration, spin-coupling, and orbital coefficients. This enables rigorous optimization of basis-set exponential parameters even for fully orthogonal multiconfiguration wave functions. Test calculations are carried out, with optimized even-tempered basis sets, on Li(2) and on the CH radical. For the latter, special attention is paid to the electronic spin density at the nuclei. 相似文献
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FE Menéndez Aránzazu Espina Camino Trobajo José R. García Julio Rodríguez 《Journal of inclusion phenomena and macrocyclic chemistry》1994,15(3):215-230
The intercalation reactions betweenn-alkylamines and -titanium phosphate in aqueous media have been investigated. The compounds with the maximum intercalation have the formula -Ti(HOPO3)2 · 2 C
n
H
2n+1
NH2 · H2O (n=1–10). Defined crystalline phases with lower amine content are described, the general formula being -Ti(HOPO3)2 ·
m
C
n
H
2n+1
NH2 ·pH2O (m=1.0 1.3, 1.5, 1.7). Whenm=1.0 then-alkylamines form a monomolecular layer. Whenm>1.0 the layer is bimolecular. The inclination angle and the packing density of then-alkylamines in the interlayer space is determined. 相似文献
10.
Fabio E. Penotti 《International journal of quantum chemistry》1996,59(5):349-378
An ab initio procedure for the calculation of atomic and molecular electronic wave functions, the Optimized-Basis-Set Multi-Configuration Spin-Coupled (OBS-MCSC) method, is generalized by introducing a separate linear combination of spin functions for each configuration, turning it into the OBS-GMCSC method. The ability to use a second-order minimization procedure in the computation of the wave function is maintained through appropriate generalization of the analytic expressions for the first and second derivatives of the energy with respect to the optimization parameters, as is the optional inclusion among the latter of the basis-function exponential parameters. The generalization, a variational improvement of the wave function, strengthens the connection with classical VB theory, of which the method can now be considered an optimized-orbitals variant, while maintaining the link with single-configuration Spin-Coupled theory, of which it may still be considered a multiconfiguration extension. The method can also be viewed as a nonorthogonal variant of the MCSCF approach. To demonstrate its practical feasibility and usefulness, the OBS-GMCSC method is applied to a study of the electronic structure and electron affinity of boron. © 1996 John Wiley & Sons, Inc. 相似文献