Electric field gradients have been measured at substitutional lattice sites in ternary semiconductors using Perturbed γ-γ Angular Correlation spectroscopy (PAC). The experimental results for AIBIIIC2VI chalcopyrite structure compounds and 2AIIB2IIIC4VI defect chalcopyrites are compared with ab-initio calculations. The latter were carried out with the WIEN code that uses the Full Potential Linearized Augmented Plane Wave method within a density functional theory. The agreement between experiment and theory is in most cases very good. Furthermore, the anion displacements in AgGaX2-compounds (X: S, Se, Te) have been determined theoretically by determining the minimum of the total energy of the electrons in an elementary cell.