Tetragonal equilibrium states of iron

First-principles total-energy calculations on tetragonal Fe show that the ferromagnetic and antiferromagnetic phases have tetragonal equilibrium states with c/a > 1, the fee value. The bulk layers of an epitaxial film of Fe on Cu(001), which are almost fee with the Cu lattice constant, are shown to be stable in the antiferromagnetic phase, but inherently unstable in the ferromagnetic phase. The structure of tetragonal equilibrium antiferromagnetic Fe is estimated to be a = 3.47 Angstrom, c = 3.75 Angstrom. [S0163-1829(99)04125-9].