[Pw_forum] ionic phase calculation(for polarization) of cubic and tetragonal PbTiO3

[sathya subramanyan]

Dear Developers,
                I am a new user of Espresso-4.0 and when I ran the example10 (polarizayion of cubic PbTiO3 via Berry phase calculation)I found that the total ionic phase is not the sum of the ionic phases of the individiual constituents i.e Pb ,Ti ,O but in the tetragonal PbTiO3 the total ionic phase is -0.22375 which is the individual sum of Pb ,Ti, O.
                            I am attaching the O/P files (only a section as the complete file is bulky)of cubic and tetra phase of PbTiO3 ( polarization calculation ) for comparison. 

                            I would be really thankful for any explanations or reasoning in this context.


FOR CUBIC PHASE

              IONIC POLARIZATION
                              ~~~~~~~~~~~~~~~~~~

        Note: (mod 1) means that the phases (angles ranging from
        -pi to pi) have been mapped to the interval [-1/2,+1/2) by
        dividing by 2*pi; (mod 2) refers to the interval [-1,+1)

  ============================================================================
    Ion    Species    Charge              Position                Phase
  ----------------------------------------------------------------------------
    1        Pb      14.000      0.0000  0.0000  0.0100    0.14000 (mod 2)
    2        Ti      12.000      0.5000  0.5000  0.5000    0.00000 (mod 2)
    3        O        6.000      0.0000  0.5000  0.5000    -1.00000 (mod 2)
    4        O        6.000      0.5000  0.5000  0.0000    0.00000 (mod 2)
    5        O        6.000      0.5000  0.0000  0.5000    -1.00000 (mod 2)
  ----------------------------------------------------------------------------
                                              IONIC PHASE:  0.14000 (mod 2)
  ============================================================================



FOR TETRAGONAL PbTiO3
            IONIC POLARIZATION

                              ~~~~~~~~~~~~~~~~~~

        Note: (mod 1) means that the phases (angles ranging from
        -pi to pi) have been mapped to the interval [-1/2,+1/2) by
        dividing by 2*pi; (mod 2) refers to the interval [-1,+1)

  ============================================================================
    Ion    Species    Charge              Position                Phase
  ----------------------------------------------------------------------------
    1        Pb      14.000      0.0000  0.0000  0.0100    0.13142 (mod 2)
    2        Ti      12.000      0.5000  0.5000  0.5377    0.05689 (mod 2)
    3        O        6.000      0.5000  0.5000  0.1118    0.62968 (mod 2)
    4        O        6.000      0.0000  0.5000  0.6174    -0.52267 (mod 2)
    5        O        6.000      0.5000  0.0000  0.6174    -0.52267 (mod 2)
  ----------------------------------------------------------------------------
                                              IONIC PHASE:  -0.22735 (mod 2)
  ============================================================================


Thanking You


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


  


  

                                  
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