Effect of local Coulomb interactions on the electronic structure and exchange interactions in Mn12 magnetic molecules -: art. no. 184435

We have studied the effect of local Coulomb interactions on the electronic structure of the molecular magnet Mn-12 acetate within the LDA+U approach. The account of the onsite repulsion results in a finite energy gap that is in a good agreement with the experimental results. The resulting magnetic moments and charge states of nonequivalent 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 Mn-12 acetate.