Using density functional theory calculations of periodic slabs, within the generalised gradient approximation, this study provides optimised structures for all plausible terminations of copper(ii) chloride surfaces along the three low-index orientations. The ab initio atomistic thermodynamic approach serves to construct a thermodynamic stability diagram for CuCl 2 configurations as a function of the chemical potential of chlorine (Δµ Cl (T, P)). We observe a shift in thermodynamic stability ordering at around Δµ Cl (T, P) = -1.0 eV between a copper-chlorine terminated (001) surface (i.e., (001)CuCl) and a (001) chlorine-covered surface (i.e., (001)Cl). This conclusion accords with experimental observations that report CuCl-bulk like structures, acting as a prerequisite for the formation of CuCl 2 -bulk like arrangements in the course of copper chlorination. Profound stabilities and optimised structures of (001)CuCl and (001)Cl configurations are discussed within the context of the functionality of CuCl 2 as the chief chlorination and condensation catalyst of aromatic pollutants under conditions relevant to their formation in thermal systems, i.e. 400-1000 K, a total operating pressure of 1.0 atm and P Cl 2 = 10 -6 -10 -4 atm (1.0-100.0 ppm).