Tetragonal equilibrium states of iron

First-principles total-energy calculations on tetragonal Fe show that the f erromagnetic and antiferromagnetic phases have tetragonal equilibrium state s with c/a > 1, the fee value. The bulk layers of an epitaxial film of Fe o n 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 fe rromagnetic phase. The structure of tetragonal equilibrium antiferromagneti c Fe is estimated to be a = 3.47 Angstrom, c = 3.75 Angstrom. [S0163-1829(9 9)04125-9].