Ab initio study of basic material properties of Fe, Co, and Ni ferromagnetic crystals

Basic material properties of bcc Fe, hcp Co, fcc Ni ferromagnetic crystals in static equilibrium condition have been calculated from first principles within DFT and SDFT. Plane-wave basis set and norm-conserving pseudopotentials have been used. An extensive comparative study of pseudopotentials has been performed which covered: the exchange–correlation (XC) functionals, the pseudopotential hardness, and the size of the model core. The model of the XC functional and the quality of the model core turned out to have substantial influence on the calculated material parameters. Thus, those two factors have been subjected to systematic analysis. The general tendency has been observed that the inclusion of spin leads to an increase of the lattice constants and a decrease of the bulk modulus. A strong influence of the quality of the model core on magnetization has been noticed: with increasing size of the model core the magnetization decreases. The effect depends on the atomic number and in Co (LSDA) and Ni is dramatic, i.e. a sudden and very rapid drop of magnetization occurs.