title: Localized overlap algorithm for unexpanded dispersion energies.
abstract: First-principles-based, linearly scaling algorithm has been developed for calculations of dispersion energies from frequency-dependent density susceptibility (FDDS) functions with account of charge-overlap effects. The transition densities in FDDSs are fitted by a set of auxiliary atom-centered functions. The terms in the dispersion energy expression involving products of such functions are computed using either the unexpanded (exact) formula or from inexpensive asymptotic expansions, depending on the location of these functions relative to the dimer configuration. This approach leads to significant savings of computational resources. In particular, for a dimer consisting of two elongated monomers with 81 atoms each in a head-to-head configuration, the most favorable case for our algorithm, a 43-fold speedup has been achieved while the approximate dispersion energy differs by less than 1% from that computed using the standard unexpanded approach. In contrast, the dispersion energy computed from the distributed asymptotic expansion differs by dozens of percent in the van der Waals minimum region. A further increase of the size of each monomer would result in only small increased costs since all the additional terms would be computed from the asymptotic expansion.
authors.affiliation: Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: Fazle
authors.initials: F
authors.lastname: Rob
authors.affiliation: School of Physics and Astronomy, Queen Mary, University of London, London E1 4NS, United Kingdom.
authors.forename: Alston J
authors.initials: AJ
authors.lastname: Misquitta
authors.affiliation: Institute of Chemistry, University of Silesia, Szkolna 9, 40-006 Katowice, Poland.
authors.forename: Rafał
authors.initials: R
authors.lastname: Podeszwa
authors.affiliation: Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Szalewicz