Structural properties of copper halides

Full potential linearized augmented plane wave method (FP-LAPW) is applied to study the elastic and the bonding properties of CuCl, CuBr, and CuI. A numerical first principles calculation of the elastic constants is used to calculate C-11,C- C-12, and C-44 for these compounds. The equilibrium lattice constant and the modulus are also given. Our FP-LAPW calculations were performed to evaluate the total energy as a function of strain, after which the data were fitted to a polynomial function of strain to determine the modulus. The experimental results of elastic constants are available only for CuCl. For CuBr and CuI, the results are compared with the available theoretical works with good agreement. In addition, we discuss the bonding character in terms of charge density, which show the strong localisation of charge around the anion side. The calculated ionicity parameter agrees with the expected estimation from the charge density behavior and compared well with the Phillips' ionicity scale. (C) 2001 Elsevier Science B.V. All rights reserved.