Fermi surface of iron under pressure

Abstract

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 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 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 /kbar for the spin-up electron s-d piece,-10 /kbar for the spin-down hole octahedron at symmetry point H, 10 /kbar for the spin-up hole pockets at point H and the electron octahedron at point I, and 10 /kbar for the spin-down electron ball.

Electronic structure of grain boundaries in the Fe86-Mn12.7-C1.3alloy

“…From Table 2 it also follows that the exchange splitting values obtained by us well agree with predictions of other authors [3][4][5][6][7][8][9][10]. Good agreement has also been attained between our prediction and the experimental value for the splitting of the crystal term P 4 [11].…”

“…The electron density obtained for the atomic configuration and used for the calculation of the electronic spectrum of a crystal [2], provides an agreement both with predictions of other authors [3][4][5][6][7][8][9][10] and with experiment [11].…”

“…Thus, the atomic base used can serve as a good zero approximation for investigating other physical characteristics of a ferromagnetic crystal. Table 3, and in Table 4 the superscripts "a" and "b" refer to the nonrelativistic calculations [9] and to the semirelativistic calculations [9], respectively. …”

Parametrisation of the LCAO Bandstructure of BCC Transition Metals

“…Neglect of the spin-orbit interactions, as assumed in recent calculations of the bandstructure of ferromagnetic iron (Tawil and Callaway 1973;Johnson et al 1984), leads to two separate sets of spin-up and spin-down energy bands. These two completely independent sets of bands can then each be described, as in the paramagnetic case, by a 9x9 LCAO model Hamiltonian, and the parameters defining these tight-binding representations determined by our direct parameter fitting set.…”

“…Cornwell et al (1968) and Boyer et al (1977), for example, have both included four additional parameters in their LCAO model Hamiltonian descriptions of the BCC transition metals in order to represent the third neighbour s-s, s-p and s-d interactions. In more recent work, Papaconstantopoulos and his co-workers Johnson et al 1984) have incorporated all 17 third neighbour interactions into their least-squares optimisation procedure in order to obtain extremely accurate bandstructure fits for some of the BCC transition metals. The extension of our direct-parameter fitting scheme to progressively larger parameter sets, however, will always be bounded by the number of linearly independent energy level expressions that can be obtained from diagonalisation of the LCAO model Hamiltonian.…”