(345d) Catalysis On Transition Metal Oxides: Which Methods Should We Be Using?
Transition metal oxides are already widely used in conventional heterogeneous catalysis, and are increasingly being investigated for use in photo- and electrochemically driven catalytic processes. It is therefore highly desirable to be able to carry out accurate density functional theory calculations on these materials. Unfortunately, transition metal oxides present substantial challenges for density functional theory. Traditional GGA functionals fail dramatically for surprisingly simple systems, for example erring by an order of magnitude in predicting the band gap of stoichiometric nickel oxide. Consequently, many efforts have been undertaken to improve the performance of GGA functionals. Approaches have included mixing some exact Hartree-Fock exchange into the calculation (as typified by the HSE functional), incorporation of the kinetic energy density (as in the M06-L functional), and application of an electron delocalization penalizing function, as in the DFT+U method. In this talk, we discuss the relative advantages and disadvantages of each of these approaches when applied to calculations on transition metal oxides, drawing specific examples from calculations performed on oxides of nickel, molybdenum, and vanadium, and a bismuth vanadate - bismuth molybdate solid solution.