We show that under well-defined conditions the Hohenberg-Kohn theorem (HKT) that provides the foundation of ground-state density functional theory (DFT) can be extended to the lowest-energy resonance of unbound electronic systems. The extended version of the HKT provides an adequate framework to carry out DFT calculations of negative electron affinities.

• Received 12 December 2006

DOI:https://doi.org/10.1103/PhysRevLett.98.093003