Binding energy of the ring form of (H2O)6: Comparison of the predictions of conventional and localized-orbital MP2 calculations

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Abstract
The binding energy of the ring form of (H2O)6 is calculated by means of the MP2 and localized‐orbital MP2 (LMP2) methods. The LMP2 method is found to be effective at reducing basis set superposition error in the electron correlation contribution to the binding energy. The inclusion of f and g functions on the O atoms and d and f functions on the H atoms leads to an increase of about 3.2 kcal/mol in the stability of the ring form of (H2O)6. Our best estimate of the binding energy is −44.3 kcal/mol. Of this, three‐body interactions contribute −11.60 kcal/mol, and the four‐ , five‐ , and six‐body interactions combined contribute −2.0 kcal/mol. Although inclusion of electron correlation energy is crucial for obtaining an accurate value of the two‐body interactions, the net effect of electron correlation on the three‐ and higher‐body interactions is only about 0.2 kcal/mol. Based on these results, a computationally efficient strategy for obtaining accurate binding energies of hydrogen‐bonded clusters is proposed.