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 α-Mn that has been reported previously in experiments. This new phase of strained α-Mn exhibits a noncollinear spin structure with large magnetic moments.

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The stability of the nonmodulated martensitic phase, the austenitic Fermi surface and the phonon dispersion relations for ferromagnetic Ni2MnGa are studied using density functional theory. Exchange-correlation effects are considered with various degrees of precision, starting from the simplest local spin density approximation (LSDA), then adding corrections within the generalized gradient approximation (GGA) and finally, including the meta-GGA corrections within the strongly constrained and appropriately normed (SCAN). We discuss a simple procedure to reduce a possible overestimation of magnetization and underestimation of nesting vector in SCAN by parametrically decreasing self-interaction corrections.