title: GW and Bethe-Salpeter study of small water clusters.
abstract: We study within the GW and Bethe-Salpeter many-body perturbation theories the electronic and optical properties of small (H2O)n water clusters (n = 1-6). Comparison with high-level CCSD(T) Coupled-Cluster at the Single Double (Triple) levels and ADC(3) Green's function third order algebraic diagrammatic construction calculations indicates that the standard non-self-consistent G0W0@PBE or G0W0@PBE0 approaches significantly underestimate the ionization energy by about 1.1 eV and 0.5 eV, respectively. Consequently, the related Bethe-Salpeter lowest optical excitations are found to be located much too low in energy when building transitions from a non-self-consistent G0W0 description of the quasiparticle spectrum. Simple self-consistent schemes, with update of the eigenvalues only, are shown to provide a weak dependence on the Kohn-Sham starting point and a much better agreement with reference calculations. The present findings rationalize the theory to experiment possible discrepancies observed in previous G0W0 and Bethe-Salpeter studies of bulk water. The increase of the optical gap with increasing cluster size is consistent with the evolution from gas to dense ice or water phases and results from an enhanced screening of the electron-hole interaction.
authors.affiliation: CNRS, Institut NEEL, F-38042 Grenoble, France.
authors.forename: Xavier
authors.initials: X
authors.lastname: Blase
authors.affiliation: CNRS, Institut NEEL, F-38042 Grenoble, France.
authors.forename: Paul
authors.initials: P
authors.lastname: Boulanger
authors.affiliation: CEA, DEN, Service de Recherches de Métallurgie Physique, F-91191 Gif-sur-Yvette, France.
authors.forename: Fabien
authors.initials: F
authors.lastname: Bruneval
authors.affiliation: Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794-3800, USA.
authors.forename: Marivi
authors.initials: M
authors.lastname: Fernandez-Serra
authors.affiliation: INAC, SP2M/L_Sim, CEA/UJF Cedex 09, 38054 Grenoble, France.
authors.forename: Ivan
authors.initials: I
authors.lastname: Duchemin