DFT calculations on the electronic structures of BiOX (X = F, Cl, Br, I) photocatalysts with and without semicore Bi 5d states

✍ Scribed by Wen Lai Huang; Qingshan Zhu

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 509 KB
• Volume: 30
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/jcc.21055

✦ Synopsis

Abstract

The electronic structures of BiOX (X = F, Cl, Br, I) photocatalysts have been calculated with and without Bi 5__d__ states using the experimental lattice parameters, via the plane‐wave pseudopotential method based on density functional theory (DFT). BiOF exhibits a direct band gap of 3.22 or 3.12 eV corresponding to the adoption of Bi 5__d__ states or not. The indirect band gaps of BiOCl, BiOBr, and BiOI are 2.80, 2.36, and 1.75 eV, respectively, if calculated with Bi 5__d__ states, whereas the absence of Bi 5__d__ states reduces them to 2.59, 2.13, and 1.53 eV successively. The calculated gap characteristics and the falling trend of gap width with the increasing X atomic number agree with the experimental results, despite the common DFT underestimation of gap values. The shapes of valence‐band tops and conduction‐band bottoms are almost independent of the involvement of Bi 5__d__ states. The indirect characteristic becomes more remarkable, and the conduction‐band bottom flattens in the sequence of BiOCl, BiOBr, and BiOI. Both O 2__p__ and X np (n = 2, 3, 4, and 5 for X = F, Cl, Br, and I, respectively) states dominate the valence bands, whereas Bi 6__p__ states contribute the most to the conduction bands. With the growing X atomic number, the localized X np states shift closer toward the valence‐band tops, and the valence and conduction bandwidths evolve in opposite trends. Atomic and bond populations have also been explored to elucidate the atomic interactions, along with the spatial distribution of orbital density. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009