Solvation Species of Hydrated Excess Protons in Liquid Water

Solvation structures of excess protons in water are highly relevant to electric properties and for an understanding of proton transport in liquids and membranes. We present unprecedented long-time ab-initio molecular dynamics simulations using a state-of-the-art hybrid-meta GGA exchange-correlation functional to simulate the temporal evolution of an excess proton in liquid water. The functional yields excellent results for bulk water and results are compared to the state-of-the-art hybrid GGA functional rev-PBE0-D3. Our simulations suggest that protons in water are predominantly solvated within dimeric water structures and how the dimeric water solvation structure interacts with its closest water neighbor in a H₇O₃⁺ unit without persistent proton localization on a single water molecule. The findings are in close agreement with previous reports on water-ACN solvent mixtures [1,2] and unravel microscopic aspects of the asymmetric potential along the proton transfer coordinate observed in nonlinear two-dimensional infrared spectroscopy [3].



[1] Dahms et al., Science. 357, 491-495 (2017).

[2] Kundu et al., J. Phys. Chem. Lett. 10, 2287–2294 (2019).

[3] Fournier et al., Nat. Chem. 10, 932-937 (2018).