[Pw_forum] regarding born-effective charge

[himanshu at iopb.res.in]

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Respected QE users,
                    I tried to perform Born-effective charge calculation
according to the procedure given in example10 of
Example Directory. I first did scf calculation by
displacing 0.05Angstrom one of the atom along x-axis
and then did nscf calculation with options
lberry=.true.,gdr=1 and nppstr=70.

                    but i am getting NAN value, here is the output

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

        The calculation of phases done along the direction of vector 1
        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 =         NaN  (mod   8.2766587)  (e/Omega).bohr

           P =         NaN  (mod   0.0033970)  e/bohr^2

           P =         NaN  (mod   0.1942150)  C/m^2

        The polarization direction is:  ( 1.00000 , 0.00000 , -.00000 )

         System has 1.32eV band gap also. could you please suggest me how
to get the correct value of Born-effective charge.

Regards
Himanshu
IOPB