Bismuth and oxygen vacancies induce (2 x 1) reconstructions in bismuth oxyhalide (BiOX, X = Cl, Br, I) (001) surfaces

The bismuth oxyhalides (BiOX, X = Cl, Br, I) are constantly investigated due to their efficient catalytic prop-erties. Here we extend the exploration of the (001) BiOX surfaces, considering different possible surface ter-minations and defects through a comprehensive ab-initio approach. First-principles thermodynamics are used to analyze the models' stability. Results show that the Bi-terminated BiOX (1 x 1) surfaces are the most stable at Bi-rich and O-rich chemical potential conditions; At Bi-rich and O-poor conditions, the halogen-terminated BiOX (1 x 1) surfaces become stable. Furthermore, as the Bismuth chemical potential decreases, Bismuth and Oxygen vacancies stabilize the BiOX (2 x 1) surface reconstructions. The BiOX (2 x 1) reconstructions present arrays of ordered Bi and O vacancies along the [010] direction. The models' electronic properties are computed by the projected density of states, Thersoff-Hamann scanning tunneling microscopy (THSTM) images, and electrostatic potential isosurfaces. The proposed BiOX (2 x 1) surfaces could facilitate nucleophilic attacks at the O surface atoms; consequently, it could be key to promote surface catalytic reactions, such as water splitting.