Benchmark Structures and Binding Energies of Small Water Clusters with Anharmonicity Corrections
Publication Date
2011
Description
For (H2O)n where n = 1–10, we used a scheme combining molecular dynamics sampling with high level ab initio calculations to locate the global and many low lying local minima for each cluster. For each isomer, we extrapolated the RI-MP2 energies to their complete basis set limit, included a CCSD(T) correction using a smaller basis set and added finite temperature corrections within the rigid-rotor-harmonic-oscillator (RRHO) model using scaled and unscaled harmonic vibrational frequencies. The vibrational scaling factors were determined specifically for water clusters by comparing harmonic frequencies with VPT2 fundamental frequencies. We find the CCSD(T) correction to the RI-MP2 binding energy to be small (<1%) but still important in determining accurate conformational energies. Anharmonic corrections are found to be non-negligble; they do not alter the energetic ordering of isomers, but they do lower the free energies of formation of the water clusters by as much as 4 kcal/mol at 298.15 K.
Journal
Journal of Physical Chemistry A
Volume
115
Issue
43
First Page
12034
Last Page
12046
Department
Chemistry
Link to Published Version
Recommended Citation
Temelso, Berhane; Archer, Kaye A.; and Shields, George C.. "Benchmark Structures and Binding Energies of Small Water Clusters with Anharmonicity Corrections." Journal of Physical Chemistry A (2011) : 12034-12046.