[Pw_forum] negative value of polarization and Z* for Pb in Tetragonal PbTiO3 and discrepancy

[sathya subramanyan]

Dear Prof. Eyvaz,
                   Thank you very much for your reply In response to your advice regarding the inaccuracy in structure input for tetragonal PbTiO3, I checked the literature and thus have taken  the structural input parameteres(lattice constant,c/a and atomic positions)from PRL 80,1998,4321 and done the convergence test. conv_threshold used now is 1e-12
  The result is as follows.Could you please let me know whether the convergence is good or not.

THE INPUT FILE FOR TETRAGONAL PbTiO3

&control
    calculation  = 'scf'
    restart_mode = 'from_scratch'
    pseudo_dir   = '/home/nbaski/espresso-4.0.1/pseudo/'
    outdir       = '/home/nbaski/tmp/'
 /
 &system
    ibrav=6
    celldm(1)=7.373,
    celldm(3)=1.065
    nat=5
    ntyp=3
    nbnd=25
    ecutwfc=30.0
    occupations = 'fixed'
    degauss=0.00
 /
 &electrons
    conv_thr = 1e-12,
    mixing_beta=0.3,
 /
ATOMIC_SPECIES
  Pb   207.2      Pb.vdb.UPF
  Ti    47.867    Ti.vdb.UPF
  O     15.9994   O.vdb.UPF
ATOMIC_POSITIONS
  Pb    0.000    0.000    0.000
  Ti    0.500    0.500    0.538
  O     0.500    0.000    0.612
  O     0.000    0.500    0.612
  O     0.500    0.500    0.117
K_POINTS {automatic}
  4 4 4 1 1 1

                    **************
THE OUTPUT FILE(a part only as it is a heavy file) 

 highest occupied, lowest unoccupied level (ev):     9.6746   12.5554

!    total energy              =  -333.71409381 Ry
     Harris-Foulkes estimate   =  -333.71409381 Ry
     estimated scf accuracy    <        5.8E-13 Ry

     The total energy is the sum of the following terms:

     one-electron contribution =   -94.69940998 Ry
     hartree contribution      =    73.25826560 Ry
     xc contribution           =   -49.63383021 Ry
     ewald contribution        =  -262.63911922 Ry

     convergence has been achieved in  19 iterations

    

SATHYA SHEELA.S
Grad. Student
Department of Physics 
National Institute of Technology
Tiruchirapalli - 620015 
India
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