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...
