Difference in total energy between bcc and fcc iron

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Abstract
Motivated by discrepancies in recent calculations of the stability of bcc versus fcc iron, based on density-functional theory, we have investigated the effects of various approximations on the total energy of bcc and fcc iron. We find that in order to discuss phase stability on a 1 mRy/atom scale a careful analysis of the integrations in the Brillouin zone is necessary. A muffin-tin approximation to the shape of the potential and charge density induces errors of about 4 mRy/atom for the difference between fcc and bcc iron, and indicates that the effects of the atomic-sphere approximations must be investigated more thoroughly. Employing different approximations to the local-density form of the exchange and correlation energy yields changes in the relative values of the total energy of 2 mRy/atom, and hence this approximation also is important when total-energy differences are small.