Study of water cluster anions using the self-interaction corrected density functional approximations*

Accurate description of the excess charge in water cluster anions is challenging for standard semi-local and (global) hybrid density functional approximations (DFAs). Using the recent unitary invariant implementation of the Perdew-Zunger self-interaction correction (SIC) method by means of Fermi-Lowdin orbitals, we assess the effect of self-interaction error on the vertical detachment energies (vDEs) of water cluster anions with the local spin density approximation (LSDA), PBE-GGA, and the SCAN meta-GGA functionals. Removal of self interaction error corrects the electron overbinding tendency of the LSDA, PBE, and SCAN. The vDEs of water cluster anions, obtained from the total energy difference of anion and neutral, are significantly improved upon removal of self-interaction errors and are better than the hybrid B3LYP functional but fall short of MP2 accuracy. Removal of SIE results in substantial improvement to the eigenvalue of the extra electron. The negative of the highest occupied eigenvalue after SIC provides an excellent approximation to the vertical detachment energy especially for the SIC-PBE wherein the MAE of vDEs with respect to CCSD(T) is only 17 meV, the best amongst all approximations compared in this work.