Perdew-Zunger Self-Interaction Correction in Ion-Water Clusters*

We study the importance of self-interaction correction in density functional approximations for ion-water clusters, with different bonding patterns. For this purpose, we have used the Fermi-Löwdin orbital self-interaction correction (FLOSIC) [1] method to calculate binding energies (BE) of protonated water clusters (H₃O⁺(H₂O)_n, n=1-3 and 6), deprotonated water clusters (OH^-(H₂O)_n, n=1-6), small halide-water clusters (X^-(H₂O)_n, X=(F, Cl, Br), and n=1,2), and small alkali ion-water clusters (M⁺(H₂O)_n, M=(Li, Na, K), and n=1,2). We have considered three non-empirical exchange-correlation functionals namely, the local density approximation (LDA), the generalized gradient approximation (GGA) formulated by Perdew, Burke, Ernzerhof (PBE), and the strongly constrained and appropriately normed (SCAN) meta-GGA. We show that the FLOSIC method yields an improved description of BE for all systems that are connected at least with one hydrogen bond and that the error decreases with an increase in the size of an ion or equivalently decreases with the length of the hydrogen bond. However, FLOSIC strongly overestimates the bond dissociation energy of small alkali ion-water clusters.

1. M. R. Pederson, A. Ruzsinszky, and J. P. Perdew, J. Chem. Phys. 140, 121103 (2014).