[Pw_forum] a question about LDA+U

[rjxiao]

Dear all,
I am learning the LDA+U method by reading the PhD thesis of Matteo Cococcioni. I try to do the same calculation of FeO which is mentioned in the thesis. When I use the cell with 2 iron atoms (C1) and set the U=4.29eV abtained directly from the thesis, there is no energy gap appearing. Maybe it is because the interaction of the second nearest neighbours can not be described correctly in such a small cell according to the thesis.So I enlarge the model.Then I use the cell with 8 iron atoms (C4), but the self-consistency does not converge in both the calculation of U=4.29eV and of U=0eV(LDA+U is turned off) even when I change the mixing_beta to 0.1. I realy want to know where I have made mistakes.The input files are affixed.
I have puzzled by this problem for many days. I am really thankful to you for your any opinion.

----------
Input file for C1:
&CONTROL
title = 'FeO' ,
calculation = 'scf' ,
restart_mode = 'from_scratch' ,
outdir = '/home/rjxiao/tmp/' ,
pseudo_dir = '/home/rjxiao/mydir/pwscf/pseudo/' ,
prefix = 'FeO+U' ,
/
&SYSTEM
ibrav = 5,
celldm(1) = 10.026125,
celldm(4) = 0.8333333,
nat = 4,
ntyp = 3,
ecutwfc = 40 ,
ecutrho = 400 ,
occupations = 'tetrahedra' ,
degauss = 0.005 ,
smearing = 'marzari-vanderbilt' ,
nspin = 2 ,
starting_magnetization(1) = 1.0,
starting_magnetization(2) = -1.0,
starting_magnetization(3) = 0.0,
lda_plus_u = .true. ,
Hubbard_U(1) = 4.29,
Hubbard_U(2) = 4.29,
Hubbard_U(3) = 0.0,
Hubbard_alpha(1) = 0.0,
Hubbard_alpha(2) = 0.0,
Hubbard_alpha(3) = 0.0,
/
&ELECTRONS
/
ATOMIC_SPECIES
F1 55.84500 Fe.pz-nd-rrkjus.UPF 
F2 55.84500 Fe.pz-nd-rrkjus.UPF 
O 15.99940 O.pz-rrkjus.UPF 
ATOMIC_POSITIONS alat 
F1 0.000000000 0.000000000 0.000000000 
F2 0.000000000 0.000000000 1.414213500 
O 0.000000000 0.000000000 0.707106750 
O 0.000000000 0.000000000 2.121320300 
K_POINTS automatic 
4 4 4 0 0 0 

----------------------
INput file for C4:
&CONTROL
title = 'Fe4+U' ,
calculation = 'scf' ,
restart_mode = 'from_scratch' ,
outdir = '/home/rjxiao/tmp/' ,
pseudo_dir = '/home/rjxiao/mydir/pwscf/pseudo/' ,
prefix = 'FeO-C4+U' ,
/
&SYSTEM
ibrav = 5,
celldm(1) = 11.577172,
celldm(4) = 0.5,
nat = 16,
ntyp = 3,
ecutwfc = 40 ,
ecutrho = 400 ,
occupations = 'tetrahedra' ,
degauss = 0.005 ,
smearing = 'marzari-vanderbilt' ,
nspin = 2 ,
starting_magnetization(1) = 1.0,
starting_magnetization(2) = -1.0,
starting_magnetization(3) = 0.0,
lda_plus_u = .true. ,
Hubbard_U(1) = 4.29,
Hubbard_U(2) = 4.29,
Hubbard_U(3) = 0.0,
/
&ELECTRONS
mixing_beta = 0.2 ,
/
ATOMIC_SPECIES
F1 55.84500 Fe.pz-nd-rrkjus.UPF 
F2 55.84500 Fe.pz-nd-rrkjus.UPF 
O 15.99940 O.pz-rrkjus.UPF 
ATOMIC_POSITIONS crystal 
F1 0.500000000 0.500000000 0.500000000 
F1 0.000000000 0.500000000 0.500000000 
F1 0.500000000 0.000000000 0.500000000 
F1 0.000000000 0.000000000 0.500000000 
F2 0.000000000 0.000000000 0.000000000 
F2 0.500000000 0.000000000 0.000000000 
F2 0.000000000 0.500000000 0.000000000 
F2 0.500000000 0.500000000 0.000000000 
O 0.250000000 0.250000000 0.250000000 
O 0.750000000 0.750000000 0.750000000 
O 0.750000000 0.250000000 0.250000000 
O 0.250000000 0.750000000 0.750000000 
O 0.250000000 0.750000000 0.250000000 
O 0.750000000 0.250000000 0.750000000 
O 0.250000000 0.250000000 0.750000000 
O 0.750000000 0.750000000 0.250000000 
K_POINTS automatic 
4 4 4 0 0 0 


Best regards,

Sincerely,
Ruijuan Xiao
Institute of Physics,
Chinese Academy of Sciences