SOLAR: New Materials Search for Solar Energy Conversion to Fuels

Electronic structure calculations will be performed using the first principles density functional theory (DFT) based on the local density approximation (LDA) and the generalized gradient approximation (GGA). The LDA/GGA formalism, however, suffers from the well-known "gap problem". This is a serious drawback since the reliability of the optical calculations depends on the accurate determination of electronic band states. An extension of the LDA/GGA method that has been found to correct this band-gap problem is the LDA/GGA + U method, where the Hubbard paramater (U) is an on-site Coulomb repulsion parameter that incorporates part of the electron correlation absent in LDA/GGA. With an appropriate choice of U, the LDA/GGA + U method can reproduce the electronic energy band accurately.