Can anyone guide me in crystal plasticity formulation for single crystal

I have been trying to make a crystal plasticity UMAT. This is my first umat and i am kind of stuck.

I need some guidance in making the umat .

My email id is dr.krishangovind@gmail.com. I would be very helpful to you.

I am a good idea about the fundamentals required in crystal plasticity. I have tried some UMAT of my  own but they are not working fine.

Thank you