title: Electron emission from diamondoids: a diffusion quantum Monte Carlo study.
abstract: We present density-functional theory (DFT) and quantum Monte Carlo (QMC) calculations designed to resolve experimental and theoretical controversies over the optical properties of H-terminated C nanoparticles (diamondoids). The QMC results follow the trends of well-converged plane-wave DFT calculations for the size dependence of the optical gap, but they predict gaps that are 1-2 eV higher. They confirm that quantum confinement effects disappear in diamondoids larger than 1 nm, which have gaps below that of bulk diamond. Our QMC calculations predict a small exciton binding energy and a negative electron affinity (NEA) for diamondoids up to 1 nm, resulting from the delocalized nature of the lowest unoccupied molecular orbital. The NEA suggests a range of possible applications of diamondoids as low-voltage electron emitters.
authors.affiliation: TCM Group, Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, United Kingdom.
authors.forename: N D
authors.initials: ND
authors.lastname: Drummond
authors.forename: A J
authors.initials: AJ
authors.lastname: Williamson
authors.forename: R J
authors.initials: RJ
authors.lastname: Needs
authors.forename: G
authors.initials: G
authors.lastname: Galli