Quantum-chemical comprehensive study of the organophosphorus compounds adsorption on zinc oxide surfaces

Ab initio calculations at the density functional theory and the second-order Møller-Plesset perturbation theory levels, and using the n-layered integrated molecular orbital and molecular mechanics (ONIOM) method, have been performed for the adsorption of dimethyl methylphosphonate (DMMP) and tabun (GA) on (ZnO) _n (where n ) 4, 18, or 24 molecular clusters of (101̄0) and (0001) zinc oxide surfaces). Different adsorption sites and DMMP orientations were considered. Calculations include the evaluation of the optimized geometries, atomic charges, interaction energies, various methods applied, and different sizes and surface types of the ZnO fragments. On both surfaces, the molecular adsorption proceeds as chemisorption via the formation of a Zn ⋯O chemical bond in the case of the DMMP adsorption complex and a P ⋯O covalent bond or a Zn ⋯N chemical bond for GA adsorption complexes. The type of surface greatly affected the strength of the intermolecular interactions and the interaction energies. The results indicate that the adsorption of DMMP and GA is energetically more preferable on the nonpolar (101̄0) ZnO surface. GA was determined to be bound more tightly to the ZnO surface than DMMP, but the adsorption energies were approximately twice as low as the values revealed for the adsorption of GA and DMMP on the CaO surface. [Paukku, Y.; Michalkova, A; Leszczynski, J. Struct. Chem. 2008, 19 (2), 307; Michalkova, A; Paukku, Y.; Majumdar, D.; Leszczynski, J. Chem. Phys. Lett. 2007, 438, 72.] Therefore, it can be concluded that the decomposition of nerve agents and their simulants will be easier on CaO, whereas ZnO should make an efficient sensor for the detection of such compounds.