[Pw_forum] Small U for Co in ZnO for LDA+U

[Matteo Cococcioni]

Dear Shu-jun

it's not totally clear to me whether the 0.31 eV U_Co was computed and 
used with occupations of 2.6. If this is the case,
and it works as you say, this looks pretty amazing (and suspicious) to 
me (although it is another demonstration that one should look at the 
results produced with that U more than at the value of U itself). In 
fact the LDA+U functional is designed for occupations between 0 and 1.

Using U_projection_type = 'norm-atomic' is a quick, temporary solution 
to the problem but doesn't allow you to compute stresses. Hopefully
this will be fixed soon.

Matteo


??? Shu-jun Hu wrote:
> Dear All,
>
> I would post my comments on the topic of LDA+U calculation of small U_Co.
>
> (1) The self-consistently calculated U_Co is indeed sensitive to the oxidation
> state of Co. In Co-doped ZnO DMS, the value is about 0.31 eV, a very "small"
> number. However, in Co-doped SnO2, we got a "reasonable" value of 3.7 eV.
> U_projection_type is specified as the default (atomic) in both cases during the
> calculation of U_Co.
>
> (2) The calculated band structure is much sensitive to the value of U_Co and
> U_Co=0.31 eV does have a significant effect with respect to U=0. U_Co=0.31 eV can
> well fit the experimental results (APL 84 4233 (2004), and also J. Appl. Phys. 103
> 07D130 (2008)), where the occupied Co:3d majority state are deep in the valence
> band rather than in the gap. If U_Co=2 to 5 eV is implemented, Nektarios is right:
> a Co-d projected DOS far deep into the valence (completely non sense).
>
> (3) The occupation is larger than 1 but not less than 1 in the "atomic" case. A
> piece of output file is listed in the end.
>
>     Best wishes.
>
>                                              shu-jun
>
>
>
>      iteration #  1     ecut=    30.00 Ry     beta=0.30
>      Davidson diagonalization with overlap
>      ethr =  1.00E-06,  avg # of iterations =  2.0
>  enter write_ns
> U( 1) =  0.0000      U( 2) =  5.0000      U( 3) =  0.3100      U( 4) =  0.3100
> alpha( 1) =  0.0000      alpha( 2) =  0.0000      alpha( 3) =  0.0000      alpha(
> 4) =  0.0000
> atom  1   Tr[ns(na)]=  20.2308353
> atom  1  spin  1
> eigenvalues:  2.6157258 2.6161606 2.6163747 2.6230370 2.6231626
>  eigenvectors
>  1  -0.1857398  0.4838857 -0.3108623 -0.4315218  0.6697081
>  2   0.7691240 -0.1376398 -0.3613721 -0.4813049 -0.1651042
>  3  -0.6107095 -0.2857263 -0.3371356 -0.4914774 -0.4361008
>  4   0.0275961  0.8118942  0.0830406 -0.0532713 -0.5747457
>  5  -0.0148797  0.0780907 -0.8076006  0.5811597 -0.0609523
>  occupations
>  2.616  0.000  0.000  0.000  0.000
>  0.000  2.621  0.000  0.000 -0.003
>  0.000  0.000  2.621 -0.003  0.000
>  0.000  0.000 -0.003  2.619  0.000
>  0.000 -0.003  0.000  0.000  2.618
> atom  1  spin  2
> eigenvalues:  0.6259172 0.6323802 0.6442143 2.6141658 2.6196970
>  eigenvectors
>  1  -0.1040632 -0.4885801 -0.2577671 -0.3860893 -0.7314038
>  2  -0.0078294  0.2638155 -0.4985241 -0.7299864  0.3859192
>  3   0.9945218 -0.0535680 -0.0330433 -0.0447136 -0.0704671
>  4  -0.0011093 -0.4865620  0.6672800 -0.4565376  0.3310092
>  5  -0.0058854 -0.6723680 -0.4885442  0.3280686  0.4489790
>  occupations
>  0.644  0.008  0.004 -0.004 -0.007
>  0.008  1.998  0.009  0.001 -0.921
>  0.004  0.009  1.989 -0.923  0.001
> -0.004  0.001 -0.923  1.258 -0.009
> -0.007 -0.921  0.001 -0.009  1.247
>
>
>
>
>
>
>
>
>
>
> ------------------------------
> Shujun Hu                   e-mail:  hushujun at 163.com
> Shandong university         Phone:   +86/0531-88375097
> Jinan, Shandong Province, China, 250100
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