Coulomb correlation in noncollinear antiferromagnetic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>α</mml:mi></mml:math>-Mn

We discuss the interplay between magnetic and structural degrees of freedom in elemental Mn. The equilibrium volume is shown to be sensitive to magnetic interactions between the Mn atoms. While the standard generalized gradient approximation underestimates the equilibrium volume, a more accurate treatment of the effects of electronic localization and magnetism is found to solve this longstanding problem. Our calculations also reveal the presence of a magnetic phase in strained $\ensuremath{\alpha}$-Mn that has been reported previously in experiments. This new phase of strained $\ensuremath{\alpha}$-Mn exhibits a noncollinear spin structure with large magnetic moments.