The pressure dependence of the chemical bonds in copper(I) halides is studied using the DV-X alpha cluster method. The values of the bond overlap population (BOP) are discussed with varying the bond length. The different tendencies of the BOP are shown with increasing the pressure in copper(I) halides. These tendencies are discussed in connection with the p-d hybridization. (c) 2005 Elsevier B.V. All rights reserved.