Atomic and electronic structure of free niobium nanoclusters: Simulation of the M4,5-XANES spectrum of Nb13+

The atomic and electronic structure of free niobium nanoclusters has been studied on the basis of X-ray absorption near-edge structure (XANES) spectroscopy and density functional theory. M4,5-XANES spectra have been calculated for several structural models of the 13-atomic niobium cluster. The calculations have been done on the basis of both full multiple scattering theory within the muffin-tin approximation for a potential and full-potential finite difference method. The comparison of the experimental M4,5-edge XANES spectrum (Peredkov et al., J. Electron Spectros. Relat. Phenomena 184 (2011) 113-118) with the simulated X-ray absorption spectra of Nb13+ hints to a highly-symmetric icosahedral structure of the cluster. An internuclear distance of 2.2 ± 0.1 Å between neighboring “surface” atoms of the icosahedron and 2.09 Å between the central “bulk” atom and “surface” atoms, respectively, has been found upon comparison of the experimental and theoretical XANES spectra.