Cluster models Cu20 obtained by FSA and DFT strategies and XANES simulated spectrum by FDMNES

G.J. SOLDANO; Y. JOLY; ANDRINI, L.; F.G. REQUEJO; M. MARISCAL

Campinas

Otro; Annual Users Meeting LNLS/CNPEM; 2017

LNLS/CNPEM

From those years, considerableprogress in the knowledge in clusters [1] weredone, but due to the production and characterization difficulties, manyquestions remain opened. It can be said that the studies of clusters are dividedinto four main stages [1,2]: calculusmethods and theoretical cluster predictions, physical-chemistry clustergeneration, cluster detection, and cluster experiments where the cluster are probedin its applications and tested with multiple techniques. The involved clustersizes, ranging from some atoms and the nano-meter radius up, to somemillions of atoms, make their evidence at the limit of the detectiontechniques.Another aspect is that, coppernanoclusters (Cu-NCs), for example, are difficult to stabilize because ofatom-specific electron configuration, in contrast with intermetallic, such asAumAgn or AumCun isolable, whichare monodisperse and with atomically precise nature.On other hand, some authors arguethat the structure is probably the most fundamental property of a cluster andis important for understanding all aspects of chemical and physical behaviour [3] while others argue that it isthe electronic structure. [4] We will thus use in this context both absorptionedges, i.e. XANES, to get both kindsof information.We present ab initio simulations ofX-ray Absorption Near-Edge Structure spectra, performed on model Cu-NCs builtby fast simulated annealing (FSA) and optimized by Density Functional Theory(DFT) minimization. By comparison with experiments and the analysis of thesimulated spectrum shapes, we show the sensitivity of the technique on thenumber of atoms n, around 20, and on the morphology of the Cunnano-clusters. For this study we used both L3 and K edges and found the formermore sensitive. We also get a good agreement with previous predictions on theHOMO-LUMO gaps.