Structure and thermodynamics of H3O+(H2O)8 clusters: A combined molecular dynamics and quantum mechanics approach

• Published in: Computational and theoretical chemistry 2013-10, Vol.1021, p.240-248
• Main Authors: Temelso, Berhane, Köddermann, Thorsten, Kirschner, Karl N., Klein, Katurah, Shields, George C.
• Format: Article
• Language: English
• Subjects: Force field optimization; Hydrogen bonding; Hydronium; Molecular dynamics; MP2; Solvation of protons
• ISSN: 2210-271X
• DOI: 10.1016/j.comptc.2013.07.039

[Display omitted] •Molecular dynamics (MD) simulations were used to sample the low energy isomers of H3O+(H2O)8.•Ab initio calculations yielded benchmark structures and binding energies.•Box- and net-like structures were prominent at low temperatures.•Tree-like structures were dominant at high temperatures.•Calculated IR spectrum of the global minimum was consistent with experimental observations. We have studied the structure and stability of H3O+(H2O)8 clusters using a combination of molecular dynamics sampling and high-level ab initio calculations. 20 distinct oxygen frameworks are found within 2kcal/mol of the electronic or standard Gibbs free energy minimum. The impact of quantum zero-point vibrational corrections on the relative stability of these isomers is quite significant. The box-like isomers are favored in terms of electronic energy, but with the inclusion of zero-point vibrational corrections and entropic effects tree-like isomers are favored at higher temperatures. Under conditions from 0 to 298.15K, the global minimum is predicted to be a tree-like structure with one dangling singly coordinated water molecule. Above 298.15K, higher entropy tree-like isomers with two or more singly coordinated water molecules are favored. These assignments are generally consistent with experimental IR spectra of (H3O+)(H2O)8 obtained at ∼150K.