Fermi surface of iron under pressure

The augmented-plane-wave (APW) method was used to calculate spin-polarized energy bands for body-centered-cubic iron at the normal lattice constant and at lattice spacings corresponding to approximate pressures of 128 and 256 kbar. Both nonrelativistic and semirelativistic energy bands at each pressure were determined with the use of potentials that incorporated the von Barth—Hedin formalism for exchange and correlation. The APW method was used to generate the energy bands at 55 $\overrightarrow{\mathrm{k}}$ points of an irreducible wedge in the Brillouin zone; then a Slater-Koster Hamiltonian, fitted to the APW results, was used to generate the energy bands at 1785 $\overrightarrow{\mathrm{k}}$ points in the irreducible wedge and to calculate extremal areas of the Fermi surface and their pressure derivatives. To improve agreement with experiment, the first-principles spin-polarized energy bands were rigidly shifted for each lattice spacing by an amount necessary to reproduce the experimental magneton number. The orders of magnitude of the calculated pressure derivatives of the extremal areas were ${10}^{-4\mathrm{}}$/kbar for the spin-up electron $s-d$ piece, -${10}^{-4\mathrm{}}$/kbar for the spin-down hole octahedron at symmetry point $H$, ${10}^{-3\mathrm{}}$/kbar for the spin-up hole pockets at point $H$ and the electron octahedron at point $\Gamma$, and ${10}^{-2\mathrm{}}$/kbar for the spin-down electron ball.