A convergence test of the full-potential linearized augmented plane wave (FLAPW) method: Ferromagnetic bulk bcc Fe

Abstract

The convergence behavior of the all-electron full-potential linearized augmented plane-wave (FLAPW) method with the explicit orthogonalization (XO) scheme is tested on ferromagnetic bulk body-centered-cubic Fe. Applying a commonly used criterion relating the plane-wave and angular momentum cutoffs, lmax = RMTKmax, where RMT is the muffin-tin (MT) sphere radius and Kmax is the plane-wave cutoff for the basis - the total energy is converged and stable for KmaxRMT = 10. The total energy convergence dependence on the star-function cutoff, Gmax, is minimal and so a Gmax of 3Kmax or a large enough Gmax is a reasonable choice. We demonstrate that the convergence with respect to lmax or a fixed large enough Gmax and Kmax are independent, and that Kmax provides a better measure of the convergence than RMTKmax. The dependence of the total energy on RMT is shown to be small if the core states are treated equivalently, and that the XO scheme is able to treat systems with significantly smaller RMT than the standard LAPW method. For converged systems, the calculated lattice parameter, bulk modulus, and magnetic moments are in excellent agreement with the experimental values. © 2009 Journal of Magnetics.