  The electronic structure of Mn_2NiGa has been studied using density
functional theory and photoemission spectroscopy. The lower temperature
tetragonal martensitic phase with c/a= 1.25 is more stable compared to the
higher temperature austenitic phase. Mn_2NiGa is ferrimagnetic in both phases.
The calculated valence band spectrum, the optimized lattice constants and the
magnetic moments are in good agreement with experiment. The majority-spin Fermi
surface (FS) expands in the martensitic phase, while the minority-spin FS
shrinks. FS nesting indicates occurrence of phonon softening and modulation in
the martensitic phase.
