  We present a scheme for the improved description of the long-range
interatomic force constants in a more accurate way than the procedure which is
commonly used within plane-wave based density-functional perturbation-theory
calculations. Our scheme is based on the inclusion of a q point grid which is
denser in a restricted area around the center of the Brillouin Zone than in the
remaining parts, even though the method is not limited to an area around Gamma.
We have tested the validity of our procedure in the case of high-pressure
phases of bulk silicon considering the bct and sh structure.
