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In this work, we perform first principles DFT calculations to investigate theinterplay between magnetic and structural properties in Ni2MnGa. We demonstratethat the relative stability of austenite (cubic) and non-modulated martensite(tetragonal) phases depends critically on the magnetic interactions between Mnatoms. While standard approximate DFT functionals stabilize the latter phase, amore accurate treatment of electronic localization and magnetism, obtained withDFT+U, suppresses the non-modulated tetragonal structure for the stoichiometriccompound, in better agreement with the experiments. We show that the Andersonimpurity model, with Mn atoms treated as magnetic impurities, can explain thisobservation and that the fine balance between super-exchange RKKY typeinteractions mediated by Ni d and Ga p orbitals determines the equilibriumstructure of the crystal. The Anderson model is also demonstrated to capturethe effect of the number of valence electrons per unit cell on the structuralproperties, often used as an empirical parameter to tune the behavior ofNi2MnGa based alloys. Finally, we show that off-stoichiometric compositionswith excess Mn promote transitions to a non-modulated tetragonal structure, inagreement with experiments.

Origin of magnetic interactions and their influence on the structural properties of Ni2MnGa and related compounds