This variable controls whether the dipole is calculated at the
end of a self-consistent iteration. For finite systems the
default is yes. For periodic systems the default is no, unless
an electric field is being applied in a periodic direction.
The single-point Berry`s phase approximation is used for
periodic directions. Ref:
E Yaschenko, L Fu, L Resca, and R Resta, Phys. Rev. B58, 1222-1229 (1998).