Assessing the SCAN functional for itinerant electron ferromagnets

Density functional theory is a standard model for condensed-matter theory and computational material science. The accuracy of density functional theory is limited by the accuracy of the employed approximation to the exchange-correlation functional. Recently, the so-called strongly constrained appropriately normed (SCAN) [Sun, Ruzsinszky, and Perdew, Phys. Rev. Lett. 115, 036402 (2015)] functional has received a lot of attention due to promising results for covalent, metallic, ionic, as well as hydrogen- and van der Waals–bonded systems alike. In this work, we focus on assessing the performance of the SCAN functional for itinerant magnets by calculating basic structural and magnetic properties of the transition metals Fe, Co, and Ni. We find that although structural properties of bcc-Fe seem to be in good agreement with experiment, SCAN performs worse than standard local and semilocal functionals for fcc-Ni and hcp-Co. In all three cases, the magnetic moment is significantly overestimated by SCAN, and the $3d$ states are shifted to lower energies, as compared to experiments.

Figure 1

Total energy (a) and spin magnetic moments (b) for bcc-Fe as obtained with the vasp code for the SCAN (blue), PBE (red), and LSDA (black) functionals. The vertical dashed line corresponds to the experimental volume given in Table 1.

Figure 2

Total energy for nonmagnetic (NM) fcc-Fe and ferromagnetic (FM) bcc-Fe calculated with the vasp code using the SCAN functional.

Figure 3

Spin-resolved DOS for bcc-Fe calculated at the experimental volume with the vasp code for the SCAN (blue), PBE (red), and LSDA (black) functionals, where $E_F$ is the Fermi energy.

Figure 4

Total energy (a) and spin magnetic moments (b) for fcc-Ni as obtained with the vasp code for the SCAN (blue), PBE (red), and LSDA (black) functionals. The vertical dashed line corresponds to the experimental volume given in Table 1.

Figure 5

Spin-resolved DOS for fcc-Ni calculated at the experimental volume with the vasp code for the SCAN (blue), PBE (red), and LSDA (black) functionals, where $E_F$ is the Fermi energy.

Figure 6

Total energy (a) and spin magnetic moments (b) for hcp-Co as obtained with the vasp code for the SCAN (blue), PBE (red), and LSDA (black) functionals. The vertical dashed line corresponds to the experimental volume given in Table 1. In (b), the $c/a$ ratio was set to 1.62.

Figure 7

Spin-resolved DOS for hcp-Co calculated at the experimental volume with the vasp code for the SCAN (blue), PBE (red), and LSDA (black) functionals, where $E_F$ is the Fermi energy.