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

[Nektarios Lathiotakis]

Hi pwscf guys,

I have done some calculations on Co impurities in ZnO. I tried to fit U_Co
in such a
way that the caluclated Co-d projected DOS to fit experiment
(J. Appl. Phys. 103 07D130 (2008)). In this paper, they also fit U_Co.
They use VASP. The problem is that the optimal U for pwscf and VASP differ
quite a lot.

I found a projected DOS similar to the one in the above paper for
U_Co = 0.5eV which is much smaller than their value (5.5eV with VASP).
If I use their value, I get a Co-d projected DOS far deep into the valence
(completely non sense).

Any idea why the optimal U values for Co in this case are so different?
Unfortunately, their value is more common (most transition metals around
5eV).
Is it the different implementations for VASP and pwscf? Pseudopotential?

I have already tried to publish our results but the referees can not accept
the publication
based on such a small U_Co value.

Interestingly, my fitted value is very similar to the one determined self
consistently by
Hu et al, PRB 73, 245205 (2006) for the same system (0.35 eV). However, a
referee thinks that
these small U numbers are "eroneous".

I include a typical input file with just 8 k points.

Thanks
Nektarios
--------INPUT------------------------------------
 &control
              title = 'zno',
        calculation = 'scf',
              nstep = 200
       restart_mode = 'from_scratch',
             prefix = 'zno',
         pseudo_dir = '/usr/espresso-4.0/pseudo/',
             outdir = '/home/lat/tmp/',
      etot_conv_thr = 1.d-5,
         wf_collect = .true.
 /
 &system
              ibrav = 0,
          celldm(1) = 12.4172 ,
                nat = 16,
               ntyp = 3,
            ecutwfc = 50.0,
              nosym = .true. ,
               nbnd = 80 ,
        occupations = 'smearing',
            degauss = 1.d-3,
starting_magnetization(3)=1,
                   nspin=2
lda_plus_u=.true.
Hubbard_U(1)=6.5
Hubbard_U(2)=0.0
Hubbard_U(3)=0.5
 /
 &electrons
   electron_maxstep = 400,
    diagonalization = 'david',
        mixing_mode = 'plain',
        mixing_beta = 0.3,
           conv_thr = 1.0d-6
 /
&IONS
  pot_extrapolation = "second_order",
  wfc_extrapolation = "second_order",
/
ATOMIC_SPECIES
  Zn   65.38000  Zn.pbe-van.UPF
   O   15.99900  O.pbe-rrkjus.UPF
  Co   58.93320  Co.pbe-nd-rrkjus.UPF
CELL_PARAMETERS
0.500000 0.866025 0.000000
.5000000 -.8660250 0.000000
0.000000 0.000000 .8050500
ATOMIC_POSITIONS crystal
  Zn .1666666 .3333333 .0000000 0 0 0
   O .1666666 .3333333 .3792000 0 0 0
  Zn .3333333 .1666666 .5000000 0 0 0
   O .3333333 .1666666 .8792000 0 0 0
  Zn .6666666 .3333333 .0000000 0 0 0
   O .6666666 .3333333 .3792000 0 0 0
  Zn .8333333 .1666666 .5000000 0 0 0
   O .8333333 .1666666 .8792000 0 0 0
  Zn .1666666 .8333333 .0000000 0 0 0
   O .1666666 .8333333 .3792000 0 0 0
  Co .3333333 .6666666 .5000000 0 0 0
   O .3333333 .6666666 .8792000 0 0 0
  Zn .6666666 .8333333 .0000000 0 0 0
   O .6666666 .8333333 .3792000 0 0 0
  Zn .8333333 .6666666 .5000000 0 0 0
   O .8333333 .6666666 .8792000 0 0 0
K_POINTS automatic
2 2 2 0 0 0

-- 
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Dr. Nektarios N. Lathiotakis
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Theoretical and Physical Chemistry Institute
National Hellenic Research Foundation
Vass. Constantinou 48, GR-11635,
Athens, Greece
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Tel: +30 210 7273805 FAX: +30 210 7273794
Inst. secretary: +30 210 7273792, +30 210 7273795
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Web: http:www.eie.gr/nhrf/institutes/tpci/cvs/cv-lathiotakis-en.html
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