[Wien] about calculating the effective U

[yxl@email.jlu.edu.cn]

Dear usrs,
  I'm calculating the effective U using constrained-GGA method according 
to the paper written by Madsen and Novak, but i have a puzzel.
  For example i want to do GGA+U calculation for Co-doped TiO2, do i need 
calculate the value of U for FM and AFM calculation respectively? 
If i want to change the distance between Co-Co distance, do i need 
calculate the U again for this configuration?
                                              yours sincerely,
                                               hongxia