X-ray photoelectron spectroscopy (XPS) is a widely used experimental tool that provides element-specific information for both molecules and solids, but the connection between spectra and structural information is not always straightforward. In many cases, theoretical prediction of absolute core-electron binding energies (CEBEs) is needed to resolve experimental ambiguities. For this purpose there are several approaches to compute CEBEs using self-consistent field (SCF) methods such as density functional theory (DFT). Of these, the most widely used procedure is the "∆SCF" method, in which one explicitly computes a final-state determinant containing a core hole.