Semiempirical MSINDO calculations were performed for the study of structure and stability of c(4 × 2),p(3 × 2), and (1 × 1) overlayers of water on the MgO(100) surface. Born−Oppenheimer molecular dynamics(MD) techniques were used to simulate the changes in the adsorption at 300 K compared to that at 0 K. Itwas found that a partially dissociated double layer of the c(4 × 2) structure with coverage θ = 3/2 attacksthe MgO surface at 300 K. The hydroxylated (1 × 1) overlayer structure appears to be equally aggressivetoward the MgO surface at this temperature. Nucleation for the process of Mg(OH)2 formation was alsoobserved.