Combining 2d-Periodic Quantum Chemistry with Molecular Force Fields: A Novel QM/MM Procedure for the Treatment of Solid-State Surfaces and Interfaces.

The feasibility of a novel approach for the hybrid quantum mechanical/molecular mechanical (QM/MM) treatment of solid-state surfaces without the requirement of artificially keeping atoms at fixed positions is explored. In order to avoid potential artifacts of the QM/MM transition near the surface, a 2d-periodic QM treatment of the system is employed. Thus, the only QM/MM interface between atoms of the solid is along the non-periodic z-dimension. It is shown for the metal oxide and metal systems MgO(100) and Be(0001) that a properly adjusted embedding potential supplemented by adequate non-Coulombic potentials (if required) enables the application of the QM/MM framework in all-atom structure optimization and molecular dynamics (MD) simulation. The commonly employed constraint to keep at least some of the embedding atoms at fixed position is not required. Two exemplary applications of H2O on MgO(100) and H2 on Be(0001) demonstrate the applicability of the framework in exemplary MD simulation studies.