Small clusters of tin: Atomic structures, energetics, and fragmentation behavior

Ab initio electronic structure calculations on Sn-n (n less than or equal to 20) clusters using ultrasoft pseudopotentials and generalized gradient approximation for the exchange-correlation energy show the binding energies of clusters with n greater than or equal to 10 to be only about 11% less than the calculated bulk value. This is likely to be responsible for the recently reported [Phys. Rev. Lett. 85, 2530 (2000)] higher melting temperatures of these clusters than the bulk value. The growth behavior is found to differ from the one known for Si and Ge clusters at n greater than or equal to8 but 10- and 18- to 20-atom clusters are similar. The calculated lowest energy fragmentation products are in excellent agreement with experiments and suggest that the lowest energy structures, obtained here, are close to the global minima.