FPLMTO study of new phase changes in CuX (XÂ =Â Cl, Br, I) compounds under hydrostatic pressure

We study the ground-state properties of copper halides CuX (X = Cl, Br, I) and the behavior under pressure using a recent version of the full potential linear muffin-tin orbitals method (FPLMTO). It predicts the possibility of an additional local minimum in the tetragonal PbO phase for CuBr and CuI at 0.7 GPa and 01.53 GPa with a direct energy gap at Γ of about 0.678 eV and 1.265 eV respectively. The use of GGA in this work is more appropriate than LDA and correctly predicts the cubic B3 phase as ground state structure for the three binaries. Importantly, calculated transition pressure Pt revealed also the presence of PbO phase at 5.333 GPa for CuCl which is consistent with experimental reports. Other important results are that concerned with the possibility of phase transition from B3 to the hexagonal B8 phase at lower pressures (3.43, 4.11 and 6.23) GPa and from B3 to B2 at (22.96, 22.66 and 24.83) GPa respectively for CuBr, CuI and CuCl.