Predictive simulations of ionization energies of solvated halide ions with relativistic embedded Equation of Motion Coupled-Cluster Theory

Abstract: A subsystem approach for obtaining electron binding energies in the valence region and apply it to the case of halide ions (X$^-$, X = F-At) in water. This approach is based on electronic structure calculations combining the relativistic equation of motion coupled-cluster method for electron detachment (EOM-IP-CCSD) and density functional theory via the frozen density embedding (FDE) approach, using structures from classical molecular dynamics with polarizable force fields for discrete systems (in the present study, droplets containing the anion and 50 water molecules). Our results indicate one can accurately capture both the large solvent effect observed for the halides as well as the splitting of their ionization signals due to the increasingly large spin-orbit coupling of the p${3/2}$-p${1/2}$ manifold across the series, at an affordable computational cost. Furthermore, due to the quantum mechanical treatment of both solute and solvent, electron binding energies of semi-quantitative quality are also obtained also obtained for (bulk) water as by-products of the calculations for the halogens (in droplets).