Phase stability of Fe and Mn within density-functional theory plus on-site coulomb interaction approaches

Approaches based on the density-functional theory and including the on-site Coulomb interaction U have been extensively used to describe strongly correlated systems. Moreover, it has been shown that even in the case of moderate correlations, present for example in some of the 3d transition metals, this and similar methods can improve upon the local-density and generalized-gradient approximation (LDA and GGA) results. We investigate, by means of the LDA + U and GGA + U approaches, the phase stability of Fe and Mn, for which it is known that the LDA predicts a wrong ground state. In particular, we compare two different double-counting corrections, the so called fully-localized limit (FLL) and around mean-field (AMF). We find that the LDA and the LDA + UAMF do not yield the correct ground state, while the LDA + UFLL, GGA + UAMF and GGA +UFLL for specific ranges of effective U values, typically around 1 eV, give the correct phase stability, and in general, an improved description of the equilibrium volume and magnetic moment, compared to the GGA values.