The band-edge positions of BiOX (X = F, Cl, Br, I) was determined via density functional theory (DFT) for the first time by researchers from IPE-CAS. In the experiment anisotropy of band positions was founded and it can be correlated with the atomic planar density in these species.

The methods opened a new way to the determination of the band positions. The calculations were based on the plane-wave pseudopotential (PW-PP) DFT method, using the Perdew–Burke–Ernzerhof (PBE) GGA exchange–correlation functional. Ultrasoft pseudopotentials for O, F, Cl and Br and the Troullier–Martins norm-conserving pseudopotentials for I and Bi were employed. Bulk calculations were conducted using unit cells. To establish surface slabs, vacuum reference was built and the slabs were kept unrelaxed.

In the determination experiment, the planar average (PA) and macroscopic average (MA) electrostatic potentials of the slabs were tested. Different scales and vacuum level were applied. Results show strong dependence on the slab orientations. Influence of electronic polarization on the electronic work function of metals has been intensively explored, which helped to understand the current species with similar analysis. The interlayer distances, atomic density of the layers for the two slabs and the charge redistribution can reveal the orientation differences.

Present work only indicated the establishment of unrelaxed slabs, determining the bulk potential with respect to the vacuum level needs further investigation.

The band-edge energies of photocatalysts are key parameters to their photocatalytic activities, but they are hard to prepare with limited experimental data and scarce are analogous analyses. With the reality first-principles determination of the absoluteband-edge positions of BiOX (X = F, Cl, Br, I) was developed.

The results were published in Computational Materials ScienceVolume 55.