Ab initio molecular dynamics simulation of methanol adsorbed in chabazite

Ab initio molecular dynamics simulations based on density functional theory together with a plane wave basis set and Vanderbilt pseudopotentials are performed to explore the potential energy surface of a methanol molecule interacting with the Bronsted site of zeolite chabazite, In agreement with a recent study a stationary point is located which corresponds to a chemisorbed methoxonium species. However, molecular dynamics simulations at 400 K show that configurations corresponding to this structure are of minor probability, Instead, the most stable structure is a physisorbed complex in which the strongly interacting Bronsted proton is significantly delocalized in the region between the methanol and the framework oxygen of the zeolite catalyst. A stationary point on the potential energy surface corresponding to such a structure proves to be more stable than the ion pair complex by about 18 kJ/mol. (C) 1997 Elsevier Science B.V.