title: Fragment-based quantum mechanical methods for periodic systems with Ewald summation and mean image charge convention for long-range electrostatic interactions.
abstract: We describe an Ewald-summation method to incorporate long-range electrostatic interactions into fragment-based electronic structure methods for periodic systems. The present method is an extension of the particle-mesh Ewald technique for combined quantum mechanical and molecular mechanical (QM/MM) calculations, and it has been implemented into the explicit polarization (X-Pol) potential to illustrate the computational details. As in the QM/MM-Ewald method, the X-Pol-Ewald approach is a linear-scaling electrostatic method, in which the short-range electrostatic interactions are determined explicitly in real space and the long-range Ewald pair potential is incorporated into the Fock matrix as a correction. To avoid the time-consuming Fock matrix update during the self-consistent field procedure, a mean image charge (MIC) approximation is introduced, in which the running average with a user-chosen correlation time is used to represent the long-range electrostatic correction as an average effect. Test simulations on liquid water show that the present X-Pol-Ewald method takes about 25% more CPU time than the usual X-Pol method using spherical cutoff, whereas the use of the MIC approximation reduces the extra costs for long-range electrostatic interactions by 15%. The present X-Pol-Ewald method provides a general procedure for incorporating long-range electrostatic effects into fragment-based electronic structure methods for treating biomolecular and condensed-phase systems under periodic boundary conditions.
authors.affiliation: Department of Chemistry, Digital Technology Center and Supercomputing Institute, University of Minnesota, Minneapolis, MN 55455, USA.
authors.forename: Peng
authors.initials: P
authors.lastname: Zhang
authors.forename: Donald G
authors.initials: DG
authors.lastname: Truhlar
authors.forename: Jiali
authors.initials: J
authors.lastname: Gao
mesh_terms: D008958:Models, Molecular; D011789:Quantum Theory; D055672:Static Electricity; D014867:Water / Q000737:chemistry
chemical_list: D014867:Water