FePt MAE accuracy: TB2J band window vs self-consistent SOC

L1₀ FePt magnetocrystalline anisotropy (meV/f.u.) from Ouro DFT (ABACUS LCAO, PBE, DZP, 100 Ry). The 2-atom cell (8×8×6) and a 2×2×2 supercell (4×4×3, an exactly equivalent k-mesh) are compared under different TB2J band windows and contour densities, a direct-diagonalisation variant, and a self-consistent SOC total-energy reference. TB2J's former 5.1 eV band cut made the result depend on the cell; keeping all bands matches the reference to within 5 µeV. Unrelaxed fixture lattice (a = 2.73 Å, c = 3.71 Å).