Electronic-structure calculations for amorphous solids using the recursion method and linear muffin-tin orbitals: Application toFe80B20

We describe a method for performing density-functional calculations for topologically disordered condensed matter. This method combines the recursion and the linear-muffin-tin-orbital (LMTO) methods, and uses the tight-binding representation. In the present version, the LMTO matrix elements are evaluated in the atomic-sphere approximation (ASA). Various levels of approximation for the ASA Hamiltonian, such as the two-center tight-binding one, are systematically derived and tested. The method is applied to crystalline bcc Fe and to amorphous ${\mathrm{Fe}}_{80}$ ${\mathrm{B}}_{20}$. Charge self-consistency is only treated for the average Fe and the average B atoms. The Fe-B bonding is found to be covalent. A Stoner theory is derived and used to describe the ferromagnetism. The structures of our density of states for ferromagnetic ${\mathrm{Fe}}_{80}$ ${\mathrm{B}}_{20}$ agree in detail with reliable photoemission data.