Supplemented-orthogonalized-plane-wave expansion for energy-band calculations

We study the convergence of a plane-wave expansion supplemented (SOPW) by d basis functions for d states in iron [for hybridized states orthogonalized plane waves (OPW's) would be used]. We find a d basis function which leads to convergence with only two sets of plane waves (to within 0.021 Ry), whereas the d basis functions proposed by Deegan and Twose are 0.069 Ry from convergence. The advantages of the SOPW expansion over the augmented-plane-wave expansion for thin-film calculations are discussed.