USE OF CHARGE SENSITIVITY ANALYSIS IN DIAGNOSING CHEMISORPTION CLUSTERS - MINIMUM-ENERGY COORDINATE AND FUKUI FUNCTION STUDY OF MODEL TOLUENE-[V2O5] SYSTEMS

摘要

Charge sensitivity analysis (CSA) is carried out for model toluene-vanadium pentoxide chemisorption complexes involving the two-pyramidal model of the active site on the (010)-V2O5 surface. Maps of the electrostatic potential around the adsorbate and the substrate cluster are used to rationalize energetical preferences of alternative perpendicular and parallel arrangements of the toluene ring relative to the pyramid bases, known from previous SCF MO studies. The minimum-energy coordinates (MEC) in the electron population space are determined from the CSA semiempirical, finite difference atomic hardness matrix for the actual SCF MO charges in the chemisorption clusters. They represent collective charge displacements which minimize the system energy per unit change in the oxidation state of a specified atom, thus providing a convenient diagnostic tool for testing the alternative charge rearrangements and range of perturbations due to the chemisorption bond or changes in the cluster environment. The MEC relaxed hardnesses diagnose mode stabilities and together with the MEC topologies identify the most probable locations of the adsorbate activation. Finally, the atomic Fukui function indices are used to explore trends in the distribution of the external charge transfer due to the system environment. (C) 1995 John Wiley & Sons, Inc. [References: 15]