A large number of the isomers of neutral and ionic Snn（n=2-15） clusters have been designed and optimized at the level of MP2/LANL2DZ with the aid of the Gaussian 09 software package. The most stable geometric structures of ionic（cationic and anionic） Sn clusters have been compared with the corresponding neutral geometries. Most structures of Snn＋ and Snn are similar to each other except for the structures of those with n=5, 11 and 15; while the anions Snn- are almost different from Snn clusters with n=9--15 except for Sn12- and Snl4-. The electronic properties have been calculated, including binding energy, second difference in energy, HOMO-LUMO gaps, ionization potentials, and electron affinities.
The complexes formed by calcium ion and 12 common amino acids were investigated systematically in the gas phase at the level of MP2/6-311＋＋G（d,p）//MP2/6-3 1G（d,p）.The results show that the salt-bridge structure is the most preferred motif for Ca2＋ binding aliphatic amino acids without heteroatom in the side chain,while charge-solvated（CS） structure is the most preferred motif for Ca2＋ binding other amino acids except for glutamine and lysine.IR spectra of Gln-Ca2＋ and Asn-Ca2＋ complexes were calculated and compared well with the available experiments.From the study in aqueous solution,the bidentate salt-bridge structure was determined to be the most favorable for all the twenty kinds of amino acids to chelate Ca2＋ to both the oxygen atoms of the negatively carboxylate group in the backbone.
