Toward More Efficient Density-Based Adaptive Qm/Mm Methods

Adaptive QM/MM (quantum mechanical/molecular mechanical) methods repartition molecules on-the-fly into the QM and MM regions based on a partitioning criterion. A density-based partitioning scheme offers a unique way of carrying out QM and MM assignments on the presence/absence of (non) covalent interactions between non-QM core molecules and the QM core. Here, we present two improvements to promote our density-based adaptive partitioning strategy for adaptive QM/MM calculations. First, bond formation/breaking processes between non-QM core molecules and the QM core are monitored using a density-based descriptor, to define an adaptive QM core region on the fly. Second, the density-based adaptive QM/MM partitioning scheme is made efficient enough for large systems by utilizating an adaptive search region and a Voronoi style-partitioning scheme. The adaptive search region is used to preselect the subset of molecules that may interact strongly enough with the QM core region, and then a density-based interaction calculation is only carried out on this subset. A Voronoi style-partitioning scheme achieves an efficient assignment of the density-based interactions.