In this article, we motivate the detailed comparison of the physical properties of individual configurations of a ferroelectric solid solution as a means toward developing first principles models for these systems. We compare energies, dielectric constants&egr;∞,mode effective charges of local polar distortions, and the zero temperature piezoelectric behavior of several orderedPb3GeTe4supercells. Cluster expansions of these properties show the importance of second-neighbor effects, which can be related to symmetry-preserving relaxation and its effect on the symmetry breaking polar instabilities. ©1998 American Institute of Physics.