DFT+U and CP2K

The DFT+U method is tricky with CP2K and convergence issues are not uncommon. Some tips also at Convergence-CP2K may help.

Here's some other ideas.

Change Basis Set

Some basis sets are easier for convergence using the DFT+U method. My experience is that smaller basis sets converge easier. The disadvantage of smaller basis sets is less accuracy.

Use DFT+U Ramping

This is a neat method that incrementally increases the U value to the target U value.

&DFT_PLUS_U
  L 2
  U_MINUS_J 0.220496
  # U = 6 eV
  U_RAMPING 0.0220496
  #INIT_U_RAMPING_EACH_SCF .TRUE.
  #EPS_U_RAMPING 1.E-6
 &END

Use Large U Value

Sometimes it is easier to use a very large U value to generate a wavefunction with desired properties (e.g. localized electrons), and then use this wavefunction to start another calculation with lower U value.