CI and DFT Studies of the Adsorption of the Nerve Agent Sarin on Surfaces

A theoretical study is presented on the adsorption of the sarin molecule, a nerve agent, on three model solid surfaces: aliphatic (graphane), aromatic (graphene), and ionic (CaO). Calculations are carried out using accurate electronic structure methods based on configuration interaction (CI) as well as complementary density functional theory (DFT) and time dependent (TD) DFT calculations. The objective is to describe surface interactions accurately in order to identify factors that affect adsorption of sarin. Potential energy curves are calculated and compared between surface types. Computed CI binding energies to graphane, graphene, and calcium oxide surfaces are 2.2, 4.5, and 13.2 kcal/mol, respectively. The corresponding DFT binding energies are 6.4, 4.8, and 18.8 kcal/mol, respectively. Excited states of free sarin as well as sarin bound to the surfaces are examined using TDDFT and CI. Low-lying excited states of the adsorption complexes involving excitations from the surface to sarin are calculated