[Pw_forum] Calculating Hubbard U

Matteo Cococcioni matteoc at MIT.EDU
Thu Mar 2 15:28:44 CET 2006

Dear Henning,

you are right: if you set Hubbard_U and Hubbard_alpha exactly to 0 the 
code won't print the occupations and if lda_plus_u = .true. it stops with 
the error message you report. Maybe this should be changed but the way 
around this is very easy and is exactly what you were suggesting. To 
obtain the occupations printed on your output file (and to compute the 
U) just set Hubbard_U to very small values (1.d-10 is on the very safe 
side but you could use even smaller values if you prefer: it only needs to 
be non zero). I hope this helps.


On Thu, 2 Mar 2006, Henning Glawe wrote:

> 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
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