A stochastic exploration of the quantum conformational spaces in the microsolvation of divalent cations with explicit consideration of up to six solvent molecules [Mg (H₂O)n)](2+), (n=3, 4, 5, 6) at the B3LYP, MP2, CCSD(T) levels is presented. We find several cases in which the formal charge in Mg²⁺ causes dissociation of water molecules in the first solvation shell, leaving a hydroxide ion available to interact with the central cation, the released proton being transferred to outer solvation shells in a Grotthus type mechanism; this particular finding sheds light on the capacity of Mg²⁺ to promote formation of hydroxide anions, a process necessary to regulate proton transfer in enzymes with exonuclease activity. Two distinct types of hydrogen bonds, scattered over a wide range of distances (1.35-2.15 Å) were identified. We find that in inner solvation shells, where hydrogen bond networks are severely disturbed, most of the interaction energies come from electrostatic and polarization+charge transfer, while in outer solvation shells the situation approximates that of pure water clusters.
The effect of surface coverage of species, θ, on the kinetic parameters of N2, NO and N2O formation in a system simulating ammonia oxidation over Pt(111) has been studied by using periodic density functional theory (DFT). The energy barriers for product formation decrease as θ increases, with the effect being more significant above 0.25 ML. The heat of surface reaction decreases as θ increases, making the dissociation of the products less favourable due to a weaker interaction of the intermediates with the surface. The effect of θ on the binding energy is stronger for N* than for either O* or NO*, but it is more apparent in the co-adsorption with O* and NO*. Similarly, the coverage of N* more strongly affects the activation energy of N2 and N2O desorption than does the coverage of O* for NO* and N2O formation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.