Structural properties of BCC and FCC iron: LMTO-ASA-Stoner calculations

Abstract

The LMTO-ASA (Linear Muffin-Tin Orbitals - Atomic Spheres Approximation) calculations of structural properties of BCC and FCC iron were performed. The ground-state magnetic properties: ferromagnetic contributions to the total energy and magnetic moments, were found by making use of the Stoner theory of itenerant ferromagnetism, rather than spin-polarized calculations. This enabled us to circumvent the difficulty resulting from using the traditional local spin-density approximation which is known to have failed predicting correctly the energetics of iron phases. The Stoner exchange parameter, I, was calculated from the linear response theory as a function of volume. Then a constant enhancement factor, β, was introduced and the new Stoner parameter, β βI, was used in all the calculations. The factor β was found by fitting the equilibrium atomic volume of the ferromagnetic BCC phase to its experimental value. No other adjustments of any quantities were performed. The calculations revealed that the nonmagnetic BCC modification was unstable with respect to the spontaneous magnetization. Ferromagnetism stabilizes the BCC phase. The calculated bulk moduli, magnetic moments and the BCC-FCC energy difference are in good agreement with the available experimental data.