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

[胡树军 Shu-jun Hu]

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










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Shujun Hu                   e-mail:  hushujun at 163.com
Shandong university         Phone:   +86/0531-88375097
Jinan, Shandong Province, China, 250100