Development and Application of a Hybrid QM/MM Method for the Computational Investigation of Reactions At Metal/Water Interfaces

Computational investigations of chemical reactions at metal/water interfaces pose a unique challenge of properly accounting for the effect of a liquid-phase environment on free energies of reactants, products and transition states while keeping the computational model simple enough to warrant its practical application. In this paper, we propose and validate a hybrid QM/MM method for computation of the effect of an aqueous-phase environment on the heat of reaction of a metal catalyzed reaction step.  By treating only the reaction zone and its immediate environment quantum mechanically (QM) for higher accuracy and the remainder of the metal surface and the bulk of the liquid water at the classical molecular mechanical (MM) level of theory, computational speedup of multiple orders of magnitude can be realized. Using the C-C cleavage in double-dehydrogenated ethylene glycol on the Pt (111) surface as a model reaction, we first show that it is indeed possible to correctly predict the heat of reaction in water through a combination of density functional theory (DFT) calculations on periodic-slab and non-periodic-cluster models. Then, we demonstrate that the same effect can also be described within the framework of periodic embedded electrostatic cluster models (PEECM) coupled with molecular dynamics (MD) simulations of the MM subsystem. This scheme based on a combination of plane-wave (PW), PEECM and MD calculations quickly converges with QM cluster size to within a few kJ/mol of the results of complete ab-initio simulations.