Abstract: 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.