Ab initio study of the bcc-hcp transformation in iron

We present a first-principles study of four magnetic phases of iron along a transformation path connecting the bcc and hcp structures at various atomic volumes using the generalized gradient approximation. The total energies and magnetic moments are calculated using the full-potential method and are displayed in contour plots as functions of the parameter of the path and volume; borderlines between various magnetic phases are shown. A low-symmetry antiferromagnetic state with a total energy lower than that of the equilibrium nonmagnetic hcp state is found. A comprehensive picture of the martensitic transition from cubic to orthorhombic iron including both the magnetic and the structural degrees of freedom is presented, and an alternative three-stage mechanism is proposed.