  We have studied the effect of local Coulomb interactions on the electronic
structure of the molecular magnet Mn12-acetate within the LDA+U approach. The
account of the on-site repulsion results in a finite energy gap and an integer
value of the molecule's magnetic moment, both quantities being in a good
agreement with the experimental results. The resulting magnetic moments and
charge states of non-equivalent manganese ions agree very well with
experiments. The calculated values of the intramolecular exchange parameters
depend on the molecule's spin configuration, differing by 25-30% between the
ferrimagnetic ground state and the completely ferromagnetic configurations. The
values of the ground-state exchange coupling parameters are in reasonable
agreement with the recent data on the magnetization jumps in megagauss magnetic
fields. Simple estimates show that the obtained exchange parameters can be
applied, at least qualitatively, to the description of the spin excitations in
Mn12-acetate.
