Interactions of tabun (GA) with non-hydroxylated and hydroxylated CaO clusters have been studied using density functional (DFT) and Moller-Plesset second order perturbation (MP2) levels of theory. The nature of interactions has been further investigated from the topology of charge distribution (using Atoms in Molecules formalism) and molecular electrostatic potential (MEP) surfaces. These adsorption studies indicate that GA adsorbs strongly on the non-hydroxylated CaO cluster through its P=O bond, while interactions of GA on the hydroxylated cluster are weak. These model studies could thus be useful to characterize inorganic oxides for efficient detection and disposal of GA. (c) 2007 Elsevier B.V. All rights reserved.