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 cutos, l max = R MT K max , where R MT is the mun-tin (MT) sphere radius and K max is the plane-wave cuto for the basis—the total energy is converged and stable for K max R MT = 10. The total energy convergence dependence on the star function cuto, 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 R MT K max . 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.