Refine
Has Fulltext
- no (2)
Year of publication
- 2013 (2) (remove)
Document Type
- Article (2)
Language
- English (2)
Is part of the Bibliography
- yes (2) (remove)
Keywords
- Car-Parrinello (1)
- ab initio (1)
- density functional theory (DFT) (1)
- hemibond (1)
- hydroxyl radical (1)
Institute
Despite the critical importance of the hydroxyl radical in major scientific fields, there are still open questions on the behavior of this species in the aqueous phase. In particular, there has been much debate on the existence of a hemibonded interaction between the hydroxyl radical and water molecules. While some reports indicate that the hemibonded radical might explain some experimental data, others have claimed that this interaction is simply a density functional theory (DFT) artifact. Here, we provide results from high level (basis set limit of coupled-cluster levels up to single, double, triple excitations (CCSD(T)) and beyond) ab initio calculations of different OH center dot(H2O)(n) clusters in the gas phase to accurately explore the existence of the hemibonded interaction and its energy difference with respect to other well-defined hydrogen bond interactions. Additional comparisons with second order perturbation theory (MP2) and DFT are also presented. Constrained molecular dynamics was applied to determine the free energy for the formation/disruption and ice systems. Overall, our findings confirm that the hemibond can be an alternative structure for the hydroxyl radical in the condensed phase when the formation of hydrogen bonds is impeded. These results will aid the understanding of theoretical and experimental data and help future experimental designs for the detection of this important species.
Assessment of coupled cluster theory and more approximate methods for hydrogen bonded systems
(2013)
To assess the accuracy of post-Hartree-Fock methods like CCSD(T), MP3, MP2.5, MP2, SCS-MP2, SOS-MP2, and DFT-SAPT, we evaluated several effects going beyond valence-correlated CCSD(T). For 16 small hydrogen bonded systems, CCSD(T) achieves an RMS error of 0.17 kJ/mol in the dissociation energy compared to our best estimate, which is a composite method akin to W4 theory. The error of CCSD(T) is thus much lower than for atomization energies. MP2 is surprisingly accurate for these systems with an RMS error of 1.3 kJ/mol. MP2.5 yields a clear improvement over MP2 (RMS of 0.5 kJ/mol) but still has an error about 3 times as large as CCSD(T) for the absolute RMS and almost 10 times as large for the relative RMS. error. Neither SCS-MP2, SOS-MP2, nor DFT-SAPT yield lower errors than MP2. With a Delta CCSD(T) correction to MP2, the basis set limit is readily achieved when employing diffuse functions-without these, the convergence is rather slow.