Interaction of water with small Fen clusters

The electronic and geometrical structures of clusters formed by a single water molecule and small iron clusters Fen, Fen-,andFen+, for n = 1-4, are studied using density functional theory. We found that FeH2O and Fe2H2O possess a large number of isomers with different geometries, which are close in total energy to the corresponding ground states. In accord with previous computations, the ground state of FeH2O has an inserted HFeOH geometry and water remains intact in the ground state of the FeH2O+ cation. Beginning with Fe2H2O, the lowest energy states correspond to isomers with a fully dissociated water molecule, except for the ground state of the Fe2H2O+ cation that contains an OH group. Except for FeH2O+ and Fe4H2O+, the hydrogen desorption energies (FenH2O → FenO + H2) are smaller than the water desorption energies (FenH2O → Fen + H2O) for all neutral and ionic species considered and are relatively low, being about 1.5 eV.