Low‐lying energy isomers and global minima of aqueous nanoclusters: Structures and spectroscopic features of the pentagonal dodecahedron (H2O)20 and (H3O)+(H2O)20

Abstract

AbstractWe rely on a hierarchical approach to identify the low‐lying isomers and corresponding global minima of the pentagonal dodecahedron (H2O)20 and the H3O+(H2O)20 nanoclusters. Initial screening of the isomers is performed using classical interaction potentials, namely the Transferable Interaction 4‐site Potential (TIP4P), the Thole‐Type Flexible Model, versions 2.0 (TTM2‐F) and 2.1 (TTM2.1‐F) for (H2O)20 and the Anisotropic Site Potential (ASP) for H3O+(H2O)20. The nano‐networks obtained with those potentials were subsequently refined at the density functional theory (DFT) with the Becke‐3‐parameter Lee–Yang–Parr (B3LYP) functional and at the second order Møller–Plesset perturbation (MP2) levels of theory. For the pentagonal dodecahedron (H2O)20 it was found that DFT (B3LYP) and MP2 produced the same global minimum. However, this was not the case for the H3O+(H2O)20 cluster, for which MP2 produced a different network for the global minimum when compared to DFT (B3LYP). The low‐lying networks of H3O+(H2O)20 correspond to structures having 9 ‘free’ OH bonds and the hydronium ion on the surface of the nanocluster. The IR spectra of the various networks are further analysed in the OH stretching (‘fingerprint’) region and the various bands are assigned to structural arrangements of the underlying hydrogen bonding network. © 2012 Canadian Society for Chemical Engineering