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, l(max) RMTKmax, where R-MT is the muffin-tin (MT) sphere radius and K-max 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, G(max), is minimal and so a G(max) of 3K(max) or a large enough G(max) is a reasonable choice. We demonstrate that the convergence with respect to l(max) or a fixed large enough G(max) and K-max are independent, and that K-max provides a better measure of the convergence than RMTKmax. The dependence of the total energy on R-MT 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 R-MT 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.