title: Quantum Monte Carlo calculations of nanostructure optical gaps: application to silicon quantum dots.
abstract: Quantum Monte Carlo (QMC) calculations of the optical gaps of silicon quantum dots ranging in size from 0 to 1.5 nm are presented. These QMC results are used to examine the accuracy of density functional (DFT) and empirical pseudopotential based calculations. The GW approximation combined with a solution of the Bethe-Salpeter equation performs well but is limited by its scaling with system size. Optical gaps predicted by DFT vary by 1-2 eV depending on choice of functional. Corrections introduced by the time dependent formalism are found to be minimal in these systems.
authors.affiliation: Lawrence Livermore Laboratory, Livermore, California 94550, USA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Williamson
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Grossman
authors.forename: Randolph Q
authors.initials: RQ
authors.lastname: Hood
authors.forename: Aaron
authors.initials: A
authors.lastname: Puzder
authors.forename: Giulia
authors.initials: G
authors.lastname: Galli