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

• Received 6 November 2018

DOI:https://doi.org/10.1103/PhysRevLett.121.266001