The structure of Li+, Na+, K+, Mg2+, Ca2+, Ni2+ and La3+ exchanged zeolite is studied using periodic ab initio and cluster model calculation by density functional theory (DFT). Periodic calculation is performed to monitor the cation migration in the zeolite lattice. A correlation to monitor the strength of Lewis acidity of the cations is established by Fukui function based reactivity descriptors. The activity order does not depend on the size of the cations, but depends on the localized geometry of the cations. The Lewis acidity order for different cation site considered is derived and compared with the experimental trend. (C) 2003 Elsevier B.V. All rights reserved.