LBERRY, IGPAR, NPPSTR, DIPOL tags

Setting LBERRY= .TRUE. in the INCAR file switches on the evaluation of the usual Berry phase expression for the electronic polarization of an insulating groundstate system, as modified for the application of USPP's and PAW datasets (see Refs. [61], [62] and [63]). In addition, the following keywords must be specified in order to generate the mesh of ${\bf k}$-points:

• 
  IGPAR = 1|2|3
  

  This tag specifies the socalled parallel or ${\bf G}_{\parallel}$ direction in the integration over the reciprocal space unit cell.

• 
  NPPSTR = number of points on the strings in the IGPAR direction
  

  This tag specifies the number of ${\bf k}$-points on the strings ${\bf k}_j = {\bf k}_{\perp} + j{\bf G}_{\parallel}/{\rm NPPSTR}$ (with $j=0,..,{\rm NPPSTR}-1$).

• 
  DIPOL = center of cell (fractional coordinates)
  

  This tag specifies the origin with respect to which the ionic contribution to the dipole moment in the cell is calculated. When comparing changes in this contribution due to the displacement of an ion, this center should be chosen in such a way that the ions in the distorted and the undistorted structure remain on the same side of DIPOL (in terms of a minimum image convention).