Structures, energetics and vibrational spectra of (H2O)32 clusters: a journey from model potentials to correlated theory

Empirical model potentials are found to be very useful for generating most competitive minima of large water clusters, whereas correlated (e.g. second order-MOller-Plesset perturbation (MP2) theory or higher) calculations are necessary for predicting their accurate energetics and vibrational features. The present study reports the structures and energetics of (H2O)(32) clusters at MP2 level using aug-cc-pvDZ basis set, starting with low-lying structures generated from model potentials. Such high-end and accurate calculations are made feasible by the cost-effective fragment-based molecular tailoring approach (MTA) in conjunction with the grafting procedure. The latter is found to yield electronic energies with a sub-millihartree accuracy with reference to their full calculation counterparts. The vibrational spectra of nine low-lying (H2O)(32) isomers are obtained from the corresponding MTA-based Hessian matrix. All these low-lying isomers show almost similar spectral features, which are in fair agreement with the experiment. The experimental spectrum of (H2O)(32) is thus better understood from the vibrational features of this set of very closely spaced isomers. The present case study of (H2O)(32) clearly demonstrates the efficacy in obtaining accurate structures, energetics and spectra at correlated level of theory by combining model potential-based structures with fragmentation methods.