[Pw_forum] Calculating Hubbard U

[Henning Glawe]

Moin,
I follow the Cococcioni/de Gironcoli procedure to estimate the Hubbard U for
the Cu in bulk CaCuO_2; however, the first step, the self consistent
calculation with Hubbard_U=Hubbard_alpha=0 fails with the error message:

     from setup : error #         1
     lda_plus_u calculation but Hubbard_l not set

I tracked this down to espresso-3.0/PW/setup.f90:854; for me, it looks like
you can't do a LDA+U calculation when setting U or Alpha exactly to zero for
all atoms.
How much error would it introduce setting U for the Cu to say, 1d-10 and
then varying alpha to determine the 'real' U?

-- 
c u
henning