Accurate Modeling of Water Clusters with Density-Functional Theory Using Atom-Centered Potentials.

The ability of atom-centered potentials (ACPs) to improve the modeling of water clusters using density-functional methods is explored. Water-specific ACPs were developed using accurate ab initio reference data to correct the deficiencies of the BHandHLYP density functional in the calculation of absolute and relative binding energies of water clusters. In conjunction with aug-cc-pVTZ basis sets and with or without dispersion corrections, it is possible to obtain absolute binding energies for water clusters containing up to 10 HO molecules to within 0.44 kcal/mol or 0.04 kcal/mol per water molecule. In contrast, dispersion-corrected BHandHLYP/aug-cc-pVTZ predicts binding energies with errors as large as 6 kcal/mol for (HO) in the absence of ACPs. Therefore, the ACPs improve predicted binding energies in these clusters by more than an order of magnitude. The conformers of (HO) and (HO) were used to validate the application of ACPs to larger clusters. ACP-based approaches are able to predict the binding energies in (HO) within a range of 0.3-2.2 kcal/mol (less than 1.3%) of recently revised ab initio wave function results. ACPs for basis sets smaller than aug-cc-pVTZ are also presented. However, the ability of the BHandHLYP/ACP approach to predict accurate binding energies deteriorates as the size of the basis sets decreases. Nevertheless, ACPs improve predicted binding energies by as much as a factor of 50 across the range of the basis sets studied. The BHandHLYP/aug-cc-pVTZ-ACP method was applied to (HO) in order to identify the minimum-energy structure of a collection of proposed global minimum-energy structures. The BHandHLYP/aug-cc-pVTZ-ACP approach is an accurate and computationally affordable alternative to wave function theory methods for the prediction of the binding energies and energy ranking of water clusters.