Full-potential generalized gradient approximation calculations of spiral spin-density waves in γ-Fe

Using two different forms of the generalized gradient approximation (GGA) for exchange and correlation, we have performed ab initio full-potential calculations of spiral spin-density waves in gamma-Fe for wave vectors q =(2 pi/a)(0,0,alpha) and q = (2 pi/a)(gamma,0,1). We conclude that whereas the local spin-density approximation is merely missing gradient corrections, the GGA contains gradient terms which. although a great improvement in most cases, are inherently incorrect when applied to spiral spin-density waves. [S0163-1829(99)05009-2].