A second generation of empirical potentials is produced for α-Fe within the framework of the magnetic potential formalism (Dudarev and Derlet 2005 J. Phys.: Condens. Matter 17 7097). A materials database that, in addition to ab initio-derived point defect formation energies, now includes third-order elastic constant and ab initio-derived string potential data controlling, respectively, the thermal expansion properties and the core structure of the 1/2(111) screw dislocation. Three parameterizations are presented in detail, all of which exhibit positive thermal expansion and produce a non-degenerate configuration for the relaxed 1/2(111) screw dislocation easy core structure. These potentials, along with two other published potentials, are investigated in terms of defect formation volume, early stage dislocation loop clustering energetics, (110) dumbbell interstitial diffusion, and the zero-stress 1/2(111) screw dislocation Peierls barrier and its corresponding kink formation energies.