Tetragonal equilibrium states of Mn and Fe have been found by total-energy
calculations at constant volume as a function of c/a with the full-potentia
l linearized-augmented-plane-wave method using two different potentials: (1
) the local-spin-density approximation without relativistic corrections and
(2) the Perdew-Burke-Ernzerhof exchange-correlation potential in a general
ized-gradient approximation with relativistic corrections. Comparison of po
tential (1) with potential (2) shows that the energy curves relative to the
lowest minimum of each are very similar and have minima at the same c/a va
lues. However, potential (2) makes the magnetic phases more magnetic. Both
Mn and Fe are shown to have stable and metastable tetragonal equilibrium st
ates in each of several magnetic phases. The antiferromagnetic (AF) energy
versus c/a curve of Mn shows a stable tetragonal state at c/a=0.96, close t
o the experimental value for gamma-Mn at c/a=0.95, and a metastable body-ce
ntered-tetragonal state at c/a=0.60. However the bcc state at c/a=0.707 is
inherently unstable. The calculation on Fe in tetragonal structure shows th
at AF Fe has a tetragonal equilibrium state at c/a=1.08, and ferromagnetic
Fe has a tetragonal equilibrium state at c/a=1.17. (C) 2000 American Instit
ute of Physics. [S0021-8979(00)33908-1].