Browsing by Author "Toro Labbe, A"

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    Molecular structure and bonding of copper cluster monocarbonyls CunCO (n=1-9)
    (AMER CHEMICAL SOC, 2006) Poater, A; Duran, M; Jaque, P; Toro Labbe, A; Sola, M
    In this work we analyze CO binding on small neutral copper clusters, Cu-n (n = 1-9). Molecular structures and reactivity descriptors of copper clusters are computed and discussed. The results show that the condensed Fukui functions and the frontier molecular orbital theory are useful tools to predict the selectivity of CO adsorption on these small clusters. To get further insight into the CO binding to copper clusters, an energy decomposition analysis of the CO binding energy is performed. The CS symmetry of the formed CunCO clusters (n = 1-8) allows the separation between the orbital interaction terms corresponding to donation and back-donation. It is found that, energetically, the donation is twice as important as back-donation.
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    Monte Carlo simulations of the adsorption of potassium on a Cu(111) surface
    (AMER INST PHYSICS, 1998) Padilla Campos, L; Toro Labbe, A
    Monte Carlo simulations of the adsorption of potassium on a Cu(111) surface at 80 K and coverages going from theta=0.13 ' to theta=0.26 monolayer are reported. The particles interact through an adsorbate-substrate potential previously derived and through a classical adsorbate-adsorbate Morse-type potential. Interesting results concerning the nature of the adsorbed phase have been obtained: (a) We have found that the potassium adlayer is incommensurate under 1 ML coverage (theta=0.25), but it becomes commensurate at 1 ML, forming a p(2X2) adlayer with respect to the Cu substrate. (b) A procedure to determine the distribution of potassium on different adsorption sites in terms of theta has been developed with the result that top sites are the preferred sites for adsorption, although at low and medium coverages other sites are also occupied. At 1 ML only the top sites are occupied, in good agreement with the available experimental data. (C) 1998 American Institute of Physics. [S0021-9606(98)00712-0].
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    New dual descriptor for chemical reactivity
    (AMER CHEMICAL SOC, 2005) Morell, C; Grand, A; Toro Labbe, A
    In this paper, a new dual descriptor for nucleophilicity and electrophilicity is introduced. The new index is defined in terms of the variation of hardness with respect to the external potential. and it is written as the difference between nucleophilic and electrophilic Fukui functions, thus being able to characterize both reactive behaviors. It is shown that the new descriptor correctly predicts the site reactivity induced by different donor and acceptor groups in substituted phenyl molecules. Also. the Dunitz-Burgi attack on ketones and aldehydes has been revisited to illustrate the stereoselective capability of this new index. Finally, its predictive ability has been tested successfully on different series of conjugated and noncojugated carbonyl compounds.
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    Towards understanding the molecular internal rotations and vibrations and chemical reactions through the profiles of reactivity and selectivity indices: an ab initio SCF and DFT study
    (TAYLOR & FRANCIS LTD, 2003) Chattaraj, PK; Gutierrez Oliva, S; Jaque, P; Toro Labbe, A
    Ab initio SCF and DFT(B3LYP) calculations are performed with 6-311G** basis sets for obtaining insights into molecular internal rotations in HXNX (X=O,S), different vibrational modes in water and double proton transfer reaction in (HONO)(2). While chemical reactivity is analyzed in terms of the pro. le of the global reactivity parameters, such as energy, chemical potential, hardness, polarizability, molecular valency and electrophilicity indices, the site selectivity is understood through the variations in local descriptors, such as the Fukui function and atomic valency. Principles of maximum hardness and molecular valency and the minimum polarizability principle are found to be valid in almost all cases. Rotational isomerization reactions can be better characterized by making use of the maximum hardness principle along with Hammond's postulate. Extremum points in electrophilicity during internal rotations, vibrations and chemical reaction can be located from those of chemical potential and hardness. The Fukui function and atomic valency show inverse behaviour in most cases.
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    Using Sanderson's principle to estimate global electronic properties and bond energies of hydrogen-bonded complexes
    (AMER CHEMICAL SOC, 2000) Gutierrez Oliva, S; Jaque, P; Toro Labbe, A
    In this paper, we use Sanderson's geometric mean equalization principle for electronegativity (chi) to derive expressions for molecular hardness (eta) and its derivative (gamma) that are used to estimate the electronic properties of 14 molecules and bimolecular hydrogen-bonded complexes. Beyond the determination of electronic properties, it is shown that Sanderson's scheme can be very useful as a method for rationalizing chemical reactions when both N and upsilon change. We have found that the conditions of maximum hardness and minimum polarizability complement the minimum energy criterion for stability of molecular aggregates. Finally, we propose a new scheme for obtaining molecular properties from the isolated fragments that produces results that are in excellent agreement with those determined through Sanderson's scheme.
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    Validity of the minimum polarizability principle in molecular vibrations and internal rotations: An ab initio SCF study
    (AMER CHEMICAL SOC, 1999) Chattaraj, PK; Fuentealba, P; Jaque, P; Toro Labbe, A
    Molecular vibrations in ammonia (NH3) and hydrogen sulfide (H2S), and internal rotations in hydrogen peroxide (HOOH), hydrogen thioperoxide (HSOH), hydrogen persulfide (HSSH), and ethylene (C2H4) are studied using ab initio SCF methods at the Hartree-Fock level using:a-standard Pople 6-311G** basis set. Polarizability values are calculated using both Pople's and Sadlej's basis sets, Any nontotally symmetric distortion in bond length or bond angle along the vibrational symmetry coordinates of a molecule around its equilibrium geometry decreases the equilibrium hardness value and increases the:equilibrium polarizability value, During rotational isomerization the minimum energy conformation corresponds to the maximum hardness and minimum polarizability values and the maximum energy conformation corresponds to the minimum hardness and maximum polarizability values, Density functional calculations confirm these observed trends, In general we have found that the conditions of maximum hardness and minimum polarizability complement the minimum energy criterion for molecular stability.