Two-dimensional copper thio- and seleno-cyanates.

Based on density-functional theory calculations we identify two-dimensional (2D) forms of copper thio-cyanate (CuSCN) and copper seleno-cyanate (CuSeCN). CuSCN is known to crystallize in two three-dimensional polymorphs, the beta wurtzite and the alpha structure, both with tetrahedral bonding networks. Here we find that CuSCN and CuSeCN may be stabilized also in monolayer geometries with SCN or SeCN groups protruding out of Cu planes. The cohesive energies of stacks made out of these sheets are comparable to those of the alpha and beta structures, so, in principle, 2D CuSCN and CuSeCN may be formed under the appropriate experimental conditions. Other 2D CuSCN and CuSeCN phases with honeycomb-like structures also correspond to local energy minima, but are less stable with respect to the above-mentioned systems.