Electronic structure of ferromagnetic hcp cobalt. I. Band properties

A first-principles self-consistent, unrestricted Hartree-Fock, hybridized-tight-binding-plane-wave, electronic-structure calculation for ferromagnetic cobalt in hexagonal-close-packed structure is presented. The nonlocal Hartree-Fock exchange-interaction matrix elements were explicitly included in the Hamiltonian matrix and correlation effects on the one-electron energy levels were incorporated through the pair correlation energies among the core, $3d$, and conduction electrons. The most important correlation effect was that associated with the $3d$-band electrons and this was included through the Hubbard-Kanamori bandwidth-dependent model. Self-consistency was reached through an iterative procedure with respect to the density matrix, bandwidth, and the magnetic moment. For the latter, we obtained a value of 1.58μB as compared to the experimental value of 1.56μB. We have utilized the results of our energy-band calculations to study different energy- and wave-function-related properties, namely, the work function, electronic density of states, bandwidth and exchange splittings, specific heat, Fermi-surface cross sections, and spin-wave spectra, results for which are presented here and comparisons made with experiment. Our results for a number of other properties will be presented in subsequent papers.