By fitting a potential of modified Finnis–Sinclair type to the thermal expansion of ferromagnetic Fe and paramagnetic Cr, the stability of the <110> self-interstitial atom was obtained. The resulting potentials were relatively hard, yielding high self-interstitial atom formation energies. Less hard potentials gave lower interstitial formation energy, but predicted too small a thermal expansion. It was also shown that the formation energy of the <111> self-interstitial atom depended upon the distances between the 2nd and 3rd neighbours. By raising the value of the pair potential in this region, the energy difference with respect to the <110> configuration calculated with VASP in the PAW approximation could be reproduced.

Relation between Thermal Expansion and Interstitial Formation Energy in Pure Fe and Cr. J.Wallenius, P.Olsson, C.Lagerstedt: Nuclear Instruments and Methods in Physics Research B, 2005, 228[1-4], 122-5