title: Benchmarking Density Functional Based Tight-Binding for Silver and Gold Materials: From Small Clusters to Bulk.
abstract: We benchmark existing and improved self-consistent-charge density functional based tight-binding (SCC-DFTB) parameters for silver and gold clusters as well as for bulk materials. In the former case, our benchmarks focus on both the structural and energetic properties of small-size AgNand AuNclusters (N from 2 to 13), medium-size clusters with N = 20 and 55, and finally larger nanoparticles with N = 147, 309, and 561. For bulk materials, structural, energetics and elastic properties are discussed. We show that SCC-DFTB is quite satisfactory in reproducing essential differences between silver and gold aggregates, in particular their 2D-3D structural transitions, and their dependency upon cluster charge. SCC-DFTB is also in agreement with DFT and experiments in the medium-size regime regarding the energetic ordering of the different low-energy isomers and allows for an overall satisfactory treatment of bulk properties. A consistent convergence between the cohesive energies of the largest investigated nanoparticles and the bulk's is obtained. On the basis of our results for nanoparticles of increasing size, a two-parameter analytical extrapolation of the cohesive energy is proposed. This formula takes into account the reduction of the cohesive energy for undercoordinated surface sites and converges properly to the bulk cohesive energy. Values for the surface sites cohesive energies are also proposed.
authors.forename: Luiz F L
authors.initials: LFL
authors.lastname: Oliveira
authors.affiliation: CEMES CNRS UPR 8011 , 29 rue Jeanne Marvig, BP 94347, 31055 Toulouse Cedex 4, France.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Tarrat
authors.forename: Jérôme
authors.initials: J
authors.lastname: Cuny
authors.affiliation: CEMES CNRS UPR 8011 , 29 rue Jeanne Marvig, BP 94347, 31055 Toulouse Cedex 4, France.|Université de Toulouse (UPS) , 118 Route de Narbonne, F-31062 Toulouse Cedex 9, France.
authors.forename: Joseph
authors.initials: J
authors.lastname: Morillo
authors.forename: Didier
authors.initials: D
authors.lastname: Lemoine
authors.forename: Fernand
authors.initials: F
authors.lastname: Spiegelman
authors.forename: Mathias
authors.initials: M
authors.lastname: Rapacioli