Atomic and electronic structures of neutral and cation Sn _n (n=2-20) clusters: A comparative theoretical study with different exchange-correlation functionals

The atomic structures and energetics of neutral and singly positively charged Sn _n ⁺ (n=2-20) clusters have been calculated using a plane wave pseudopotential method under the framework of the generalized gradient approximation of the density functional theory as well as by using the hybrid exchange-correlation functional viz., BLYP, B3LYP and B3PW91 under the LCAO-MO approach. From the results a systematic analysis has been carried out to obtain the physico-chemical properties such as atomization energies, ionization potentials and fragmentation behavior of the neutral and cation clusters. A comparison with the available experimental data shows that the results obtained from the B3PW91 functional provide an overall good agreement for all the properties calculated here. Our calculations show that the dominant channel for the fragmentation of Sn _n ⁺, n ≤ 11, clusters is the evaporation of an atom such that the charge remains on the rest of the cluster, while for larger clusters, fission into two subclusters becomes more favorable. Raman and infrared vibrational spectra have been calculated for a few selected clusters. These confirm the structural stabilities of the clusters and can provide a way to identify the atomic structures from experiments.