Interplay of Orbital and Relativistic Effects in Bismuth Oxyhalides: BiOF, BiOCl, BiOBr, and BiOI

The BiOX (X = F, Cl, Br, and I) series were investigated using hybrid density functional theory with explicit treatment of spin-orbit coupling effects and dispersion interaction. First-principles calculations were performed in the framework of density functional theory (DFT). Special attention was paid to electron-electron interactions, relativistic effects, and dispersion interactions. All solid-state calculations were performed in a plane-wave basis set using the code VASP. Complete structural optimizations were performed at a series of volumes in order to calculate the equilibrium lattice parameters. Convergence with respect to k-point sampling and plane wave energy was checked, with a cutoff of 520 eV and a k-point density found to be sufficient. To align the electronic band energies to the vacuum level, a surface-slab model was constructed and the corresponding electrostatic potential averaged along the c-direction, using the MacroDensity package. The larger EA of BiOI also results in a reduced overpotential for O2/oxygen anion splitting and can explain why BiOI is not as active for the degradation of rhodamine B than BiOBr and BiOCl.