[Pw_forum] a question about BORN Effective charges

[VineetKumar Pandey]

sir I performed phonon calculation for monolayer PbI2 . but I am getting
born effective charges calculated by two ways (one is dF/dE and other is
dPdu) , are quite different . i am sending you my input files .



 Effective charges (d Force / dE) in cartesian axis

           atom      1   I
      Ex  (       -2.21984        0.00000        0.00000 )
      Ey  (        0.00000       -2.21984        0.00000 )
      Ez  (        0.00000        0.00000       -0.36016 )
           atom      2   Pb
      Ex  (        3.72748        0.00000        0.00000 )
      Ey  (        0.00000        3.72748        0.00000 )
      Ez  (        0.00000        0.00000        0.57697 )
           atom      3   I
      Ex  (       -1.93678        0.00000        0.00000 )
      Ey  (        0.00000       -1.93678        0.00000 )
      Ez  (        0.00000        0.00000       -0.36018 )

          Effective charges (d P / du) in cartesian axis

           atom      1   I
      Px  (       -1.99748        0.00000        0.00000 )
      Py  (        0.00000       -1.99748        0.00000 )
      Pz  (        0.00000        0.00000       -0.30196 )
           atom      2   Pb
      Px  (        3.99223        0.00000        0.00000 )
      Py  (        0.00000        3.99223        0.00000 )
      Pz  (        0.00000        0.00000        0.60413 )
           atom      3   I
      Px  (       -1.99741        0.00000        0.00000 )
      Py  (        0.00000       -1.99741        0.00000 )
      Pz  (        0.00000        0.00000       -0.30197 )
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