  Ab initio calculations show that the Dzyaloshinskii-Moriya
interaction(DMI)and net magnetization per unit cell in BiFeO3 are reduced when
U is increasing from 0 to 2.9 eV, and independent of $J$. Interestingly, the
DMI is even destroyed as $U$ exceeds a critical value of 2.9 eV. We propose a
simple model to explain this phenomenon and present the nature of the rotation
of the magnetization corresponding to altered antiferrodistortive distortions
under DMI in BiFeO3.
