An ab initio study of the „ H 2 O ... 20 H + and „ H 2 O ... 21 H + water clusters

The study of the minimum Born–Oppenheimer structures of the protonated water clusters, H2O nH, is performed for n=20 and 21. The structures belonging to four basic morphologies are optimized at the Hartree–Fock, second-order many-body perturbation theory and coupled cluster level, with the 6–31G, 6-31G , and 6-311G basis sets, using the parallel ACES III program. The lowest energy structure for each n is found to be the cagelike form filled with H2O, with the proton located on the surface. The cage is the distorted dodecahedron for the 21-mer case, and partially rearranged dodecahedral structure for the 20-mer. The results confirm that the lowest energy structure of the magic number n=21 clusters corresponds to a more stable form than that of the 20-mer clusters. © 2009 American Institute of Physics. doi:10.1063/1.3231684