Density functional study of small aqueous Be2+ clusters

We investigate the structural, vibrational, and energetic properties of [Be(H20)n]2+ clusters with n = 1, 2, 3, 4, and 6 water molecules, relevant to Be2+ hydration. The Becke exchange gradient-corrected local density approximation is used in the framework of a pseudopotential representation of the core electrons and a plane wave expansion for the valence orbitals. The calculations were performed without imposing periodic boundary conditions. Good agreement with Hartree-Fock-based results is observed. We compare these data to results obtained by imposing periodic boundary conditions and find that the latter have only a minor influence on the results. The stability of the clusters at finite temperature was approached using ab initio molecular dynamics techniques. We find that the n = 6 cluster dissociates into a stable [Be(H2O)4]2+ complex with attached water molecules in the second hydration shell. The Car-Parrinello methodology used in the study can be applied without modification and with the same accuracy to study Be2+ in liquid water.