Vibrational and electronic properties of neutral and negatively charged C20 clusters

We computed vibrational and electronic properties of the cage, bowl, and ring isomers of neutral and negatively charged C-20, within density-functional theory, using fully optimized local-density and gradient-corrected geometries. Vibrational and electronic spectra exhibit distinctive features, which could be used to identify a given isomer and its charge state in molecular beams or thin films. Notable changes are observed in both the Raman and infrared spectra when going from the neutral to the charged isomers. We also calculated vibrational entropies from harmonic frequencies. Our results indicate that, above a critical temperature, the ring isomer is always stabilized by entropic effects, irrespective of the theoretical model used to compute the internal energy. In particular, gradient-corrected functionals predict both the neutral and charged ring to be the most stable isomer at all temperatures. Molecular-dynamics simulations were performed to study the geometry of the ring at high temperature. Furthermore, we rationalized photoelectron spectra of C-2n clusters, n=9-12, in terms of differences In the electronic structure For even and odd n.