Time-Independent Approaches to Density Matrix Functional Theory

I will overview recent work on time-independent approaches to single excited states in density (matrix) functional theory.In density (matrix) functional theory, there is no Hohenberg-Kohn (Gilbert) theorem for excited states, so alternative methods are necessary. These methods can either add descriptors (e.g., bifunctionals) or sacrifice universality (e.g., Coulomb-only functionals). While the approaches for density-functional theory are basically understood at this point, analogous methods for reduced density matrix approaches are mostly unknown. Building on the analogy to DFT methods for computing the energy of a single excited state, corresponding methods for one-electron density matrix functionals (i.e., natural orbital functionals) can be inferred.