(HF)m(H2O)n clusters, where m + n ≤ 8 and (HCl)m(H2O)n clusters, where m + n ≤ 6 have been optimized using density-fitted second-order Møller-Plesset perturbation theory (DF-MP2) with a correlation consistent triple-ζ basis set augmented with diffuse functions on non-hydrogen atoms and an extra set of tight d functions for chlorine (cc-pVTZ for H, aug-cc-pVTZ for F and O, aug-cc-pV(T+d)Z for Cl; denoted ha(T+d)Z). Harmonic vibrational frequencies reveal that 225 (HF)m(H2O)n and 36 (HCl)m(H2O)n unique minima (i.e., ni = 0) have been identified on the DF-MP2/ha(T+d)Z potential energy surface. Single point energy computations were also performed on the DF-MP2/ha(T+d)Z optimized geometries with explicitly-correlated coupled-cluster theory that includes all single and double substitutions as well as a perturbative estimate of the connected triple substitutions (CCSD(T)-F12) and the ha(T+d)Z basis set. The smallest clusters for which the global minimum exhibits proton transfer (i.e., F−/H3O+ and Cl−/H3O+) are (HCl)1(H2O)4 and (HF)6(H2O)1. The hydrated HCl system also displays double proton transfer minima where m = 2 and n = 2 − 4. Most of the proton transfer clusters characterized here share a common hydrogen bonding topology. Specifically, the proton donor(s) tend to accept two hydrogen bonds, while the proton acceptor(s) tend to donate two hydrogen bonds.

Intrinsic energetics of proton transfer in binary (HF)m(H2O)n and (HCl)m(H2O)n clusters

255th National Meeting (2018)

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