Thanks a lot for your contribution, I have some puzzles at the same time:

1) how to calculate energy level mu1, and mu2 in the contacts, mu1=Ef+qV/2 ???

2) In the reference literature ("Voltage Asymmetry of Spin-Transfer Torques") , the 3D dimension MTJ is modeled where the all the transver modes are summaried : 

     when calutating the current, how to conferm the integaration range over energy E