<i>Ionization potentials and fundamental gaps in atomic systems from the ensemble-DFT approach</i>

KS-DFT is a potent and extensively used theoretical framework for quantum simulations. While exact in principle, it is approximate in practice. Many of the commonly used exchange-correlation approximations (xc) deviate from the exact requirement of piecewise linearity for the energy. Disobeying this requirement causes low predictive power of the eigenvalues; specifically, the ionization potentials (IP) and fundamental gaps are underestimated. We addressed this problem by applying the ensemble generalization treatment to the Hartree-xc energy functional[1]. This treatment proved beneficial in the restoration of the IP theorem and simultaneously reintroduction of the derivative discontinuity into any approximate xc functional in selected systems[2]. Here, I present a comprehensive study of IP and the electron affinity (EA) calculations from the ensemble-generalized KS energy levels, using the ensemble LSDA and the ensemble generalized PBE-GGA approximations to all atoms and first ions in the periodic table. Even with these simple functionals, the prediction of the IP and the EA can be significantly improved. Analyzing the accuracy of results obtained for the different periodic table blocks reveals interesting trends and provides valuable insights for future functional development.