Density functional theory (DFT) is often used successfully for studying molecular structure and dynamics. However, there are several failures of local/semilocal and hybrid density functionals: predicting charge transfer excitations, polarizability of elongated systems, the chemical of bond symmetric radical cations, reaction barriers and the �wrong�/useless orbital energies. We describe the problems and briefly mention their sources (self-interaction, derivative discontinuity and nonzero curvature of ensemble-DFT energy). We then describe a first principles approach we developed that overcomes several aspects of the problems. We show examples, charge-transfer excitations, water ionization, occupied orbital energies vs ionization potentials,  HOMO-LUMO gaps vs fundamental gaps, Rydberg excitations, barriers and more. Review articles:R. Baer, E.      Livshits, and U. Salzner, '�Tuned� Range-separated hybrids in density      functional theory', Ann. Rev. Phys. Chem. 61, 85 (2010).L. Kronik, T.      Stein, S. Refaely-Abramson, and R. Baer, 'Excitation gaps of      finite-sized systems from Optimally-Tuned Range-Separated Hybrid      Functionals', Submitted  (2012) (preprint: http://www.fh.huji.ac.il/~roib/publicatia.htm).

New first-principles approach to density functional theory, "tuned" range separated hybrids: Why they work and when are they needed

244th National Meeting (2012)

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