Evolutionary Algorithm-based Crystal Structure Prediction for Copper(I) Fluoride

Despite numerous experimental studies since 1824, the binary copper(I) fluoride still remains unknown. We have carried out a crystal structure prediction for CuF using the USPEX evolutionary algorithm and a dispersion-corrected hybrid density functional method. In total about 5000 hypothetical structures were investigated. The energetics of the predicted structures were also counter-checked with local second-order Møller-Plesset perturbation theory. We report 39 new hypothetical copper(I) fluoride structures that are lower in energy compared to the previously predicted cinnabar-type structure. Cuprophilic Cu-Cu interactions are present in all the low-energy structures, leading to ordered Cu substructures such as helical or zig-zag-type Cu-Cu motifs. The lowest-energy structure adopts a trigonal crystal structure with space group P3121. From the electronic point of view, the predicted CuF modification is a semiconductor with an indirect band gap of 2.3 eV.