Based on the facts that the potential energy curves of the homonuclear group 12 dimers (group IIB metal) are conformal, and they can be described by the Tang-Toennies potential model, a set of combining rules are proposed for the parameters of the reduced potentials of the heteronuclear dimers. Together with the well established combining rules of the dispersion coefficients and the range parameters of the exponential repulsion, these rules enable us to determine the ground state potential energy curves of ZnCd, ZnHg, and CdHg. The determined potentials are comparable to some ab initio calculations but they are drastically different from others. (C) 2014 Elsevier B.V. All rights reserved.