Adsorption of pyridine on Lewis acid sites of microcrystalline gamma-alumina was studied by quantum chemical cluster model approach at B3LYP and HF/6-31++G(d,p) levels of theory considering both the standard and the counterpoise-corrected potential energy surfaces (PESs). Harmonic vibrational frequency shifts of pyridine v(8) and v(19) internal mode components calculated at both levels of theory seem to excellently reproduce the experimental observations, the results for standard and counterpoise-corrected PESs being essentially identical. The interaction energies of pyridine with various clusters representing microcrystalline gamma-Al2O3 were also calculated and the natural bond orbital and atoms in molecules analyses were performed. (C) 2004 Elsevier B.V. All rights reserved.