Study of odd–even effects in physisorption and chemisorption of Ar, N2, O2 and NO on open shell Ag11–13+ clusters by means of self-consistent van der Waals density functional calculations

Producción CientíficaWe have studied the adsorption and coadsorption properties of one or more X = Ar, N2, O2, and NO adsorbates on cationic silver clusters Ag11–13+, whose sizes are in the open shell region of metal clusters, aiming to understand the observed odd–even effects in the abundance spectra of Ag11–13+·mX complexes. All calculations were performed self-consistently using a non-local van der Waals correlation functional, covering the different nature of the interactions between the silver substrate and the several adsorbates, which range from dispersion (London) forces for Ar, non covalent π–π interactions for N2, charge-transfer interactions for O2 and NO, and the covalent Ag–Ag bond in the nude silver cluster. Despite the wide interval of adsorption energies, spanning two orders of magnitude, we have been able to explain the following experimental facts. For X = Ar, N2, and O2 reactions with Ag11–13+, it was observed in the mass spectra an abundance peak at n = 12 [M. Schmidt, et al., ChemPhysChem, 2015, 16, 855]. In addition it was observed the competitive adsorption of two or more N2 molecules, and the cooperative effect of adsorbing N2 together with O2 molecules. For X = NO, an abundance peak at n = 12 has been also observed [J. Ma, et al., Phys. Chem. Chem. Phys., 2016, 18, 12819]. We find that the main factors determining these properties are the different core motifs of the cluster geometry (pentagonal bipiramid for Ag11+ and Ag13+, but triangular prism for Ag12+) and, on the other hand, the odd number of valence electrons for Ag12+, leading to a smaller HOMO–LUMO gap than those of its neighbours. Further details about the preferred adsorption sites, dipole moments, and dipole polarizabilities are also discussed.Ministerio de Ciencia, Innovación y Universisades (project PGC2018-093745-B-I0)Junta de Castilla y León (programa de apoyo a proyectos de investigación - Ref. Project VA124G18)Ministerio de Economía, Industria y Competitividad (Project RYC-2014-15261

Hydrogen Chemisorption on Doubly Vanadium Doped Aluminum Clusters

Producción CientíficaThe interaction of hydrogen with doubly vanadium doped aluminum clusters, AlnV2+ (n = 1–12), is studied experimentally by time-of-flight mass spectrometry and infrared multiple photon dissociation spectroscopy. The hydrogen binding geometry is inferred from comparison with infrared spectra predicted by density functional theory and shows that for the more reactive clusters the hydrogen adsorbs dissociatively. Three sizes, n = 4, 5 and 7, are remarkably unreactive compared to the other clusters. For larger sizes the reactivity decreases, a behavior that is similar to that of singly vanadium doped aluminum clusters, and that might be attributed to geometric and/or electronic shielding of the dopants. By examining the electronic structure of Al6V2+ and Al7V2+, interactions between the frontier orbitals of the clusters and those of H2 that explain the size-dependent reactivity are identified.Ministerio de Economía, Industria y Competitividad (Project RYC-2014-15261

Static dipole polarizability of alkali-metal clusters: Electronic exchange and correlation effects

Nonlocal approximations for the electronic exchange and correlation effects are used to compute, within density-functional theory, the polarizability and surface-plasma frequencies of small jelliumlike alkali-metal clusters. The results are compared with those obtained using the local-density approximation and with available experimental data, showing the relevance of these effects in obtaining an accurate description of the surface response of metallic clusters

Surface collective oscillations of metal clusters and spheres: Random-phase-approximation sum-rules approach

Using the once and thrice energy-weighted moments of the random-phase-approximation strength function, we have derived compact expressions for the average energy of surface collective oscillations of clusters and spheres of metal atoms. The L=0 volume mode has also been studied. We have carried out quantal and semiclassical calculations for Na and Ag systems in the spherical-jellium approximation. We present a rather thorough discussion of surface diffuseness and quantal size effects on the resonance energies