Perdew-Zunger Self-Interaction Correction in Neutral, Protonated, and Deprotonated Water Clusters*

We have assessed the importance of self-interaction correction (SIC) to density functional approximations (DFA) for the description of water-ion interactions. We have used LSDA, PBE, SCAN, and the Fermi-Löwdin orbital self-interaction correction (FLOSIC)¹ in conjunction with these DFAs to calculate the binding energies of neutral, protonated [H₃O⁺(H₂O)_n], and deprotonated [OH^-(H₂O)_n] water clusters, where n denotes the number of water molecules. Including SIC is important to obtain accurate binding energies for these clusters. We find that FLOSIC-SCAN not only improves the mean absolute error in the binding energy of all clusters but also preserves the energetic ordering of the low-lying water hexamers (prism, cage, book, and cyclic) that was difficult to achieve with many non-empirical DFAs. Moreover, many-body decomposition of the total binding energy reveals that FLOSIC-SCAN significantly reduces the two-body errors in SCAN calculations. The three-body and higher-order many-body errors are also small with FLOSIC-SCAN. This shows that FLOSIC-SCAN has the potential to overcome the limitations of SCAN in describing water and aqueous ions in condensed phases.
1. M. R. Pederson, A. Ruzsinszky, and J. P. Perdew, J. Chem. Phys. 140, 121103 (2014).