On the Contribution of Vibrational Anharmonicity to the Binding Energies of Water Clusters

Abstract

The second-order vibrational perturbation theory method has been used together with the B3LYP and MP2 electronic structure methods to investigate the effects of anharmonicity on the vibrational zero-point energy (ZPE) contributions to the binding energies of (H2O)n, n = 2-6, clusters. For the low-lying isomers of (H2O)6, the anharmonicity correction to the binding energy is calculated to range from -248 to -355 cm(-1). It is also demonstrated that although high-order electron correlation effects are important for the individual vibrational frequencies, they are relatively unimportant for the net ZPE contributions to the binding energies of water clusters.

Anomalously Strong Effect of the Ion Sign on the Thermochemistry of Hydrogen Bonded Aqueous Clusters of Identical Chemical Composition

“…As seen from Figure 3 and Table 4, the difference between the harmonic and anharmonic ZPE typically does not exceed 2–3 %. This finding is in excellent agreement with the recent MP2 study [14] of pure water clusters. Another important detail is that DFT results are in good agreement with ab initio MP2 predictions.…”

Theoretical calculations: Can Gibbs free energy for intermolecular complexes be predicted efficiently and accurately?

“…Generally, the situation is quite similar as discussed earlier: there are only a few papers discussing the difference in the contribution of harmonically and anharmonically calculated frequencies in Δ S int 85, 90. The estimations that we performed using the data presented in ref 103.…”

“…Overall, the water dimer is probably the most demanded intermolecular complex ever. The most accurate calculations performed at the MP2 and CCSD(T) levels which use counterpoise‐corrected optimizations,61–63, 83, 84 total energy‐extrapolated to a CBS,71 and anharmonic values of vibrational frequencies85, 86 allow to reproduce the experimental value of the interaction energy35 and the enthalpy of formation with an uncertainty of about ±0.2–0.3 kcal/mol.…”

Mass spectrometric and quantum chemical determination of proton water clustering equilibria

“…It is also noted that theoretical binding energies of hydrogen bonded clusters without BSSE corrections often more closely reproduce experimental clustering equilibria as BSSE and basis set truncation errors cancel (Dunning, 2000;Masamura, 2001); see Xantheas (2005) for a review on BSSE correction procedures and cluster binding energies. Also, given the relatively minor contribution of vibrational anharmonicity to the binding energies in water clusters as demonstrated by Diri et al (2005) (i.e., anharmonicity corrections to theoretical binding energies of (H 2 O) 6 are less than 4 kJ mol À1 ), we have not incorporated such corrections into our theoretical results. In addition to our model chemistry calculations, we also performed density functional calculations with the B3LYP functional employing Becke's gradient corrected exchange functional, the Lee-Yang-Parr correlation functional and the 6-311G** basis set.…”