<i>Effective, Nostalgic, and Accurate: Generalized Basis Set for Core-Hole Excited State Derived from Slater’s Rule</i>

Accurate estimates of core excitation energies of molecular systems computed using quantum chemistry methods have remained elusive despite decades of published research exploring both theoretical accuracy and basis set representations. Efficient predictive approaches to this problem are of great use in the interpretation of X-ray photoelectron spectroscopy, for example. Here, we deconvolute the numerical aspects of this problem by focusing on physically motivated contracted Gaussians that better reproduce the core-excited atomic orbitals, motivated by Slater’s rules. Armed with these core-excited basis sets, total energy differences, computed via the delta-SCF methodology employing hybrid exact-exchange functionals are sufficient to reproduce core-excitation energies within experimental accuracy (~0.1eV). We also highlight a physically motivated range of variability in the core level binding energy that is naturally tied to the expectation value of the local atomic charge and which provides a more realistic estimate of accuracy and transferability of a given theory than statistical accuracy estimates based on select choices of molecules.