Requests for technical support from the VASP group should be posted in the VASP-forum.
DIPOL = [real array]
Description: specifies the center of the cell in direct lattice coordinates with respect to which the total dipole-moment in the cell is calculated.
The center of the cell w.r.t. which the total dipole-moment in the cell is calculated is specified as
DIPOL=Rx Ry Rz
where Rx, Ry and Rz are given in direct lattice coordinates.
Mind: the calculation of the dipole (IDIPOL=1-4) requires a definition of the center of the cell, and results might differ for different positions. You should use this option only for surfaces and isolated molecules. In this case use the center of mass for the position (for surface only the component normal to the surface is meaningful).
The main problem is that the definition of the dipole 'destroys' the translational symmetry, i.e. the dipole is defined as
Now, this makes only sense if drops to zero at some distance from . If this is not the case, the values are extremely sensible with respect to changes in .
Note: If the flag is not set, VASP determines, where the charge density averaged over one plane drops to a minimum and calculates the center of the charge distribution by adding half of the lattice vector perpendicular to the plane where the charge density has a minimum (this is a rather reliable approach for orthorhombic cells).