Computer simulations of chemical reactions at liquid/solid interfaces are challenging since the bond formation/rupture calls for proper description of the electronic structure using methods that are limited to small systems, such as DFT, while a description of the liquid phase requires large systems and long simulations for statistical sampling. Half a century ago, a hybrid approach referred to as QM/MM was introduced in the context of enzymatic reactions and has become widely used in simulations of biological systems [Warshel and Levitt, 1976]. An implementation of such an approach in the context of surface reactions in the presence of water will be described. There, a slab representing the surface and adsorbed atoms/molecules as well as first layer of water is included in a DFT region (the QM part) while the rest of the liquid phase is described using a polarizable potential function based on a single center multipole expansion (the MM part). Self-consistency calculations are carried out for the combined system where the electric field from the MM region is included in the DFT calculation and the electric field from the QM region is included in the polarizable potential calculation of the liquid ['Polarizable Embedding with a Transferable H2O Potential Function']. A recently developed scattering algorithm is used to keep water molecules in either the QM or MM regions ['Elastic Collision Based Dynamic Partitioning Scheme for Hybrid Simulations']. The simulations are compared with results obtained using implicit solvent and ice overlayer approximations ['Assessment of Constant-potential Implicit Solvation Calculations of Electrochemical Energy Barriers'].

Simulations of surface reactions in the presence of water using a hybrid approach combining DFT and polarizable potential function

ACS Fall 2021

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