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The flag KPOINT_BSE allows to calculate the dielectric matrix at one of the $ k-$points used to sample the Brillouine zone. In the simplest form one can specify

   KPOINT_BSE= index_of_k-point
It is best to select the desired k-point from the list of k-points in the OUTCAR file. Additionally a shift by an arbitrary reciprocal lattice vector can be supplied by specifying three additional integer numbers:
  KPOINT_BSE = index_of_k-point  n1 n2 n3
This allows the calculate the dielectric function at a k-point outside the first Brillouine zone corresponding to

$\displaystyle {\bf k} + n_1 {\bf b}_1+ n_2 {\bf b}_2 + n_3 {\bf b}_3,

where $ {\bf b}_i$ are the reciprocal lattice vectors of the unit cell.

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