Quantum Drude oscillator model for describing the interaction of excess electrons with water clusters: an application to (H2O)13(-).

Cluster anions for which the excess electron occupies an extended nonvalence orbital can be described by use of a model Hamiltonian employing quantum Drude oscillators to represent the polarizable charge distributions of the monomers. In this work, a Drude model for water cluster anions is described and used to investigate the (H2O)13(-) cluster. Several low-energy isomers are characterized, and the finite-temperature properties of the cluster are investigated by means of parallel tempering Monte Carlo simulations. Two structural motifs, one with double-acceptor water monomers and the other with four-membered rings of double-acceptor single-donor monomers with four free OH groups pointed in the same direction, are found to lead to large (approximately > eV) electron binding energies. The distributions of the computed vertical detachment energies qualitatively reproduce the experimentally measured photoelectron spectrum, and our simulations indicate that both of the main peaks in the measured spectrum derive from several isomers.