Design of Low Band Gap Double Perovskites from First Principles
  Using density functional theory (DFT)-based calculations, we propose a family of metastable, as-yet unmade V5+ and Cr6+ double perovskite compounds with low band gaps spanning much of the visible region of the solar spectrum. Through analysis of a related set of measured optical gaps of d0 ABO3 perovskites and A2B'BO6 double perovskites, an ad hoc procedure is developed to correct DFT and many-body perturbation theory gaps, bringing them into quantitative agreement with experiment for measured compounds, and predicting that V5+ and Cr6+ double perovskites would have gaps ranging from approximately 1.1-2.4 eV, significantly lower than previous materials studied in this class. DFT calculations also establish that these V5+ and Cr6+ compounds are likely able to be synthesized, either in bulk form or as epitaxial thin films. These compounds would comprise a new class of semiconducting double perovskites for potential use in solar energy conversion and other optoelectronic applications. 
Robert F. Berger and Jeffrey B. Neaton
cond-mat.mtrl-sci