Stability and electronic properties of polar and non-polar surfaces of CuI

The structural and electronic properties of polar and non-polar surfaces of CuI are investigated at the GGA-DFT level of theory. The results find that the stability of the surfaces is directly related to the interplanar distance as well as the atomic character of the terminating layer. The I-terminated surfaces are predicted to be energetically preferred. We predict the instability of the Cu-terminated (1 1 1) surface, whereas the nonpolar (1 1 0) surface shows a significant surface reconstruction with a large layer rotation angle. The Cu-terminated and I-terminated image surfaces prefer to retain their bulk-like configurations, whereas the Cu-terminated (0 0 1) and image surfaces show large deviations from their bulk configurations. The calculated band gap shows a blue or red shift of the absorption edge relative to the bulk CuI depending on the atomic nature of the terminating surface.