[Pw_forum] how to calculate the polarization of a crystal by berry phase

Jian ZHOU zjspam at gmail.com
Fri Jul 8 16:32:32 CEST 2005


Dear all, 

In the example10 of pwscf, it run a berry phase calculation and get
the Born effective charge of Pb.

However, I am now trying to calculate the polarization of a Crystal,
for example for a tetragonal BaTiO3. I firstly do a scf calculation
with the following input file:

 &control
    calculation  = 'scf'
    restart_mode = 'from_scratch'
    pseudo_dir   = '/home/zj/espresso-2.1.4/pseudo/'
    outdir       = '/root/zj/compute14/pwscf/tet_batio3'
    tstress = .true.,
 /
 &system
    ibrav=6
    celldm(1)= 7.5435
    celldm(3)=1.0110
    nat=5
    ntyp=3
    ecutwfc=30.0
    occupations = 'fixed'
    degauss=0.00
 /
 &electrons
    conv_thr = 1e-9,
    mixing_beta = 0.3d0
 /
ATOMIC_SPECIES
  O     15.9994   O.pw91-van_ak.UPF
  Ti    47.867    Ti.pw91-nsp-van.UPF
  Ba    137.327   Ba.pw91-nsp-van.UPF
ATOMIC_POSITIONS
O 0 0.5 0.48500000
O 0.5 0 0.48500000
O 0.5 0.5 -0.02500000
Ti 0.5 0.5 0.50135000
Ba 0 0 0
K_POINTS {automatic}
  4 4 4 1 1 1


And then do a berry phase calculation with the input file:

 &control
    calculation   = 'nscf'
    pseudo_dir    = '/home/zj/espresso-2.1.4/pseudo/'
    outdir        = '/root/zj/compute14/pwscf/tet_batio3'
    lberry        = .true.
    gdir          = 3
    nppstr        = 7
 /
 &system
    ibrav=6
    celldm(1)= 7.5435
    celldm(3)=1.0110
    nat=5
    ntyp=3
    ecutwfc=30.0
    occupations = 'fixed'
    degauss=0.00
 /
 &electrons
    conv_thr      = 1e-9
    mixing_beta = 0.3d0
 /
ATOMIC_SPECIES
  O     15.9994   O.pw91-van_ak.UPF
  Ti    47.867    Ti.pw91-nsp-van.UPF
  Ba    137.327   Ba.pw91-nsp-van.UPF
ATOMIC_POSITIONS
O 0 0.5 0.48500000
O 0.5 0 0.48500000
O 0.5 0.5 -0.02500000
Ti 0.5 0.5 0.50135000
Ba 0 0 0
K_POINTS {automatic}
  4 4 7 1 1 1


The final output is :

                               SUMMARY OF PHASES
                               ~~~~~~~~~~~~~~~~~

                          Ionic Phase: -0.44095 (mod 2)
                     Electronic Phase:  0.63353 (mod 2)
                          TOTAL PHASE:  0.19258 (mod 2)


                             VALUES OF POLARIZATION
                             ~~~~~~~~~~~~~~~~~~~~~~

        The calculation of phases done along the direction of vector 3
        of the reciprocal lattice gives the following contribution to
        the polarization vector (in different units, and being Omega
        the volume of the unit cell):

           P =   1.4687319  (mod  15.2529570)  (e/Omega).bohr

           P =   0.0033843  (mod   0.0351467)  e/bohr^2

           P =   0.1934880  (mod   2.0093958)  C/m^2

        The polarization direction is:  ( 0.00000 , 0.00000 , 1.00000 )


It is said that the final polarization is  0.1934880 C/m^2. And the
experiment value is about 0.26 C/m^2.  A more high cutoff energy and
more k points is tested, and found the polarization does not change
much.

So, I am not sure If the procedure is correct. If it is correct, why
the value is much smaller than the experiment one.

Thank you.

Best wishes,

Jian



More information about the users mailing list