A LCAO-LDF STUDY OF BRONSTED ACIDS CHEMISORPTION ON ZNO(0001)

The focal density functional theory coupled to the molecular cluster a pproach has been used to study the chemisorption of Bronsted acids (H2 O, H2S, HCN, CH3OH and CH3SH) on the ZnO(0001) polar surface. Geometri cal parameters and vibrational frequencies for selected species molecu larly and dissociatively chemisorbed have been computed. The agreement with literature experimental data, when available, has been found to be good. The nature of the interaction between the conjugate base of t he examined Bronsted acids and the Lewis acid site available on the su rface has been elucidated, confirming its leading role in determining the actual relative acidity scale obtained by titration displacement r eactions. The strength of this interaction follows the order OH(-)appr oximate to CN- > CH3O- > SH- > CH3S-.