[Pw_forum] CaCuO2 and LDA+U

[Chao Cao]

Dear PWSCF users and developers:

I have been trying to use PWSCF's implementation of LDA+U to calculate 
the electronic structure of CaCuO2 lately. In VASP, once I turn on U, it 
gives AFM ground state and reasonable gap separation at E_F. However, 
the procedure seems to be much harder for PWSCF. While it gets AFM gs 
correctly, I can never get a band gap. I searched the forum, and I 
realized that the initial occupation number might be important, but the 
several combinations I tried seem to give me the same result. So, is 
there any hint or suggestions, especially how to choose initial 
occupation numbers? Thanks in advance.


Best,

Chao Cao


And, here's my input file:

&control
  calculation = 'scf'
  restart_mode = 'from_scratch'
  prefix = 'CaCuO2'
  disk_io = 'low'
  outdir = './'
/
&system
  ibrav = 0, celldm(1) = 1.88972688, ntyp = 4, nat = 16
  nbnd=80, ecutwfc = 32, ecutrho = 400
  nspin = 2, starting_magnetization(2)=0.5, starting_magnetization(3)=-0.5
  lda_plus_u = .true., Hubbard_U(2) = 6.5, Hubbard_U(3) = 6.5
  occupations = 'smearing', smearing = 'mp', degauss = 0.007
/
&electrons
  mixing_beta = 0.2
  conv_thr = 1.0d-9
/
ATOMIC_SPECIES
Ca   1.0  Ca.pbe-nsp-van.UPF
Cuu  1.0  Cu.pbe-n-van.UPF
Cud  1.0  Cu.pbe-n-van.UPF
O    1.0   O.pbe-van.UPF
ATOMIC_POSITIONS crystal
Ca   0.25  0.75  0.25
Ca   0.75  0.25  0.25
Ca   0.25  0.75  0.75
Ca   0.75  0.25  0.75
Cuu  0.25  0.25  0.00
Cuu  0.75  0.75  0.50
Cud  0.75  0.75  0.00
Cud  0.25  0.25  0.50
O    0.00  0.00  0.00
O    0.50  0.00  0.00
O    0.00  0.50  0.00
O    0.50  0.50  0.00
O    0.00  0.00  0.50
O    0.50  0.00  0.50
O    0.00  0.50  0.50
O    0.50  0.50  0.50
K_POINTS automatic
  8,8,4,1,1,1
CELL_PARAMETERS cubic
   3.878393250   3.878393249   0.000000000
  -3.878393249   3.878393250   0.000000000
   0.000000000   0.000000000   6.409031058




-- 
Chao Cao

Quantum Theory Project and Department of Physics
University of Florida, Gainesville, FL 32611
U.S.A.