Structures, spectra, and electronic properties of halide-water pentamers and hexamers, X-(H2O)5,6 (X=F,Cl,Br,I):: Ab initio study

Various structures of halide-water pentamers and hexamers have been investigated using extensive ab initio calculations. Then, we compare the structures, spectra, and electronic properties of the hydrated fluoride, chloride, bromide, and iodide systems. Although some of the fluoride and iodide systems have been investigated earlier, we have carried out more accurate calculations on an enlarged conformational ensemble. The chloride-, bromide-, and iodide-water pentamers and hexamers behave somewhat similarly, but differently from the fluoride-water pentamer and hexamer. Fluoride-water clusters show semisurface (or semi-internal) structures, while chloride-, bromide-, and iodide-water clusters show surface structures. We substantiate our findings by evaluating various electronic properties such as ionization potentials, natural bond orbital charges, dipole moments, and charge-transfer-to-solvent energies, as well as vibrational frequencies of the low-energy halide-water pentamers and hexamers. (C) 2002 American Institute of Physics.