title: An Efficient Linear-Scaling Electrostatic Coupling for Treating Periodic Boundary Conditions in QM/MM Simulations.
abstract: A new linear-scaling method based on a multigrid approach to treat long-range electrostatic interactions in hybrid quantum mechanics/molecular mechanics (QM/MM) simulations is described. The scheme has been implemented in the context of a QM calculation based on density functional theory (DFT). The method is tested on an analytical model to validate the new algorithm. Two realistic problems in α-quartz crystals and a zwitterionic dipeptide (GLY-ALA) in water have been chosen as further tests. Results from QM/MM calculations with periodic boundary conditions (PBC) show that the use of PBC is essential when studying highly ordered crystal structures, unless a carefully designed MM crystal is used for the calculation. With a general shaped MM subsystem, the absence of PBC leads to an incorrect description of Kohn-Sham band gaps and charge density. The present method allows periodic boundary conditions to be used in molecular simulations of biological and material science systems.
authors.affiliation: Scuola Normale Superiore di Pisa, Piazza dei Cavalieri 7, I-56125 Pisa, Italy, and Computational Science, Department of Chemistry and Applied Biosciences, ETH Zürich, USI Campus, Via Giuseppe Buffi 13, CH-6900 Lugano, Switzerland.
authors.forename: Teodoro
authors.initials: T
authors.lastname: Laino
authors.affiliation: Scuola Normale Superiore di Pisa, Piazza dei Cavalieri 7, I-56125 Pisa, Italy, and Computational Science, Department of Chemistry and Applied Biosciences, ETH Zürich, USI Campus, Via Giuseppe Buffi 13, CH-6900 Lugano, Switzerland.
authors.forename: Fawzi
authors.initials: F
authors.lastname: Mohamed
authors.affiliation: Scuola Normale Superiore di Pisa, Piazza dei Cavalieri 7, I-56125 Pisa, Italy, and Computational Science, Department of Chemistry and Applied Biosciences, ETH Zürich, USI Campus, Via Giuseppe Buffi 13, CH-6900 Lugano, Switzerland.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Laio
authors.affiliation: Scuola Normale Superiore di Pisa, Piazza dei Cavalieri 7, I-56125 Pisa, Italy, and Computational Science, Department of Chemistry and Applied Biosciences, ETH Zürich, USI Campus, Via Giuseppe Buffi 13, CH-6900 Lugano, Switzerland.
authors.forename: Michele
authors.initials: M
authors.lastname: Parrinello