Theoretical characterization of the (H<inf>2</inf>O)<inf>21</inf> cluster: Application of an n-body decomposition procedure

Two low-energy minima of (H2O)21 with very different H-bonding arrangements have been investigated with the B3LYP density functional and RIMP2 methods, as well as with the TIP4P, Dang - Chang, AMOEBA, and TTM2-F force fields. The AMOEBA and TTM2-F model potentials give an energy ordering that agrees with the results of the electronic structure calculations, while the TIP4P and Dang - Chang models give the opposite ordering. Insight into the role of many-body polarization for establishing the relative stability of the two isomers is provided by an n-body decomposition of the energies calculated using the various theoretical methods. © 2006 American Chemical Society