  Ab initio calculations show that the coupling between
antiferrodistortive(AFD) distortions and magnetization in perovskite Bi2FeMnO6
is prohibited to make magnetization rotate as on-site Coulomb interaction($U$)
is larger than 2.7 eV, where anomalies in antiferromagnetic(AFM) vectors and
band gap varying with on-site Coulomb interaction can be observed. This
coupling is attributed to the antisymmetric Dzyaloshinskii-Moriya
interaction(DMI) driven by the eg-eg states AFM interaction and charge
redistribution with respect to different AFD distortions.
