Absolute acidities and site specific properties of zeolite catalysts modelled by advanced computational chemistry technology

Hartree-Fock structure predictions are made for two crystallographically di stinct Bronsted sites, O1H and O3H, of the zeolite catalyst H-faujasite. Th e structure optimisation adopted very large cluster models without symmetry (163 atoms; 2033 basis function) and applied the parallel TURBOMOLE code o n a multi-processor compute server. The predicted acidity strength of the t wo sites, 1166 +/- 10 kJ/mol, is the same within chemical accuracy, but - i n agreement with experiment - characteristic differences are found for the OH stretching frequencies (3617 and 3574 cm(-1)) and the H-1 NMR chemical s hifts (4.0 and 4.5 ppm). (C) 1999 Elsevier Science B.V. All rights reserved .