A quantum chemistry package for catalytic reactions, referred to as CATIVIC and based on simulation techniques of parametric Hamiltonians, is presented. We describe in detail the computational procedures for modeling adsorption on a catalytic substrate, especially the parameterization scheme using examples of atomic Al and AlOX bonds (X ϭ H, N, O, Si, Fe) for atomic and molecular parameters. The code features are illustrated with the adsorption of NO on models of ZSM-5 zeolite doped with Fe.

The formation pathways of amino acids, namely, glycine and alanine, on the surface of a polycyclic aromatic hydrocarbon flake (corone) are studied with a semiempirical, quantum-chemistry package referred to as CATIVIC. It is found that the stability of the carboxyl group (COOH) is enhanced by chemisorption that occurs in three adsorbate modes. In particular, the two-site mode enables us to make successive surface recombinations that result in chemisorbed amino-acid configurations that closely trace the surface geometry. This property imposes a strict handedness on amino acids assembled from side groups along the surface edge that, in the case of chiral surfaces, may lead to enantioselection as previously found by experiment. By comparing prospective reactions on a larger surface model (circumcoronene), evidence is found that favors amino-acid formation on the smaller flakes. Due to a lack of measurements, the main findings of the present work have been confirmed with an ab initio method.

Density functional calculations were carried to improve the calculated CO vibrational frequencies for transition metal carbonyls. Two types of density functionals were studied, hybrid and generalized-gradient methods. Using the simplex optimization method, new polarization functions for C and O atoms were obtained. With these new optimized functions, new scaling factors were obtained. The results reveal that, with the new polarization functions, the agreement between the calculated and the experimental values improves considerably. In general, the new scaling factors are very close to unit, with standard uncertainties close to Ϯ0.006 cm Ϫ1 . The use of the new polarization functions allows more precise calculations of the transition metal carbonyl CO vibrational frequencies.

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ABSTRACT:A methodology to compute the one-center integrals required for molecular calculations in parametric methods is presented. It is based on the simulated annealing technique combined with the simplex method, which are used to calculate parameterized one-center integrals in atomic systems. It is found that for an adequate selection of electronic states it is possible to obtain a set of parameters that reproduce accurately the experimental atomic excitation energies.