Based on the facts that the potential energy curves of the homo-nuclear group 2 dimers (group IIA metal), except Be-2, are conformal, and they can be described by the Tang-Toennies potential model, a set of simple combining rules are proposed for the parameters of the reduced potentials of the hetero-nuclear dimers. Together with the well-established combining rules of the range parameters of the exponential repulsion and the known dispersion coefficients, these rules enable us to determine the ground state potential energy curves of MgCa, MgSr, MgBa, CaSr, CaBa, and SrBa from those of Mg-2, Ca-2, Sr-2, and Ba-2. The determined potentials are comparable to some ab initio calculations and in excellent agreement with the experiment. (c) 2015 Published by Elsevier BV.