From one to three, exploring the rungs of Jacob’s ladder in magnetic alloys*

Magnetic systems represent an important challenge for electronic structure methods, in particular Density Functional Theory (DFT). We benchmark different exchange correlation (xc) functionals with respect to each other, and with respect to available experimental data, on two families of binary iron alloys. We climb three rungs in Jacob’s ladder of DFT (i) the local density approximation, (ii) the industry standard approximations due to Perdew, Burke and Ernzerhof, and PBEsol, and finally (iii) the meta-GGA functional SCAN. More than 400 structures in ferromagnetic and antiferromagnetic configurations were considered. We compare the Convex Hull, magnetic moment, structure, and formation energy. None of the functionals work in all conditions: the GGAs and mGGA give a fair crystal structure, but SCAN strongly overestimates the formation energy (wrt PBE and experiment). Magnetic moments are better predicted by PBE as well. Our results show that magnetic and strongly correlated materials are a tough litmus test for DFT, and that they represent the next frontier towards a truly universal xc functional.

Romero and Verstraete Eur. Phys. J. B (2018) 91 193