We have studied the structural, electronic and magnetic properties of the magnetic
shape memory alloy Ni2MnGa using Hubbard-rooted DFT+U functional and recent extensions.
Both austenite and martensite phases corresponding to high temperature and
low temperature phases respectively have been investigated. The obtained results are
compared with the results of standard DFT (GGA) calculations and available experiments.
DFT+U method is particularly useful in predicting the energy landscape of the
tetragonally distorted martensite from which the total energy minimum for c/a = 1.23,
that has been obtained with GGA functionals, but not observed in experiments, disappears.
Our results indicate that, the better description of the energitics of the tetragonal
phase can be attributed to a longer extent of localization of electrons due to the Hubbard
correction. Phonon dispersion study of austenite show a soft mode along the 
direction indicating an instability of austenite at low temperatures.