|lmax and cluster size|
lmax is the maximum angular momentum quantum number used in the calculation. This must be taken as a finite number, large enough to guarantee convergence. The figure below gives an idea of the values of lmax (lower horizontal scale) required for convergence (red curve) as a function of energy (upper horizontal scale). In addition, the figure contains the number of atoms needed for convergence in the cluster size as a function of photoelectron energy. The relation between lmax and the photoelectron energy is established by applying the criterium that 0.511 E1/2rmt~lmax, where rmt is a typical muffin-tin radius (in Å) of 1.5 Å and E is the photoelectron energy (in eV). The approximate relation between lmax and the cluster size is derived from the universal inelastic mean free path (imfp), which is in turn a function of E, by assuming a cluster of hemispherical shape and a radius equal to 1.5 times the imfp. The dashed line separates the region where EDAC is computationally faster (upper region) from that where the Rehr and Albers approach (Phys. Rev. B41, 8139 (1990)) is faster (lower region). Notice that the latter scales as N3 with the number of atoms, while EDAC scales as N2.