New Formulation of Hybrid QM/MM Method for Studying Crystalline and Amorphous Solids

We report a new formulation of hybrid QM/MM method for studying crystalline and amorphous solids that we call Seamless Multi-Layer (SML). The key feature of SML is that quantum cluster is divided into inner QM and outer QM regions, and the energy of outer QM region, containing all error prone contributions from link or boundary atoms and other sources of interface related errors is calculated at exactly the same QM level of theory as the entire QM cluster. This energy is then subtracted from SML total energy providing accurate error cancellation and making any interface parametrization unnecessary. The test calculations performed for crystalline and amorphous SiO 2 and B 2 O 3 demonstrate that even in current incomplete implementation SML approach is already suitable for studying covalent systems. At the same time calculations of Al 2 O 3 , LaF 3 and SrFCl crystals show that strong ionicity is yet challenging for new approach and require additional method development.