A general and efficient pseudopotential Fourier filtering scheme for real space methods using mask functions

A scheme for the Fourier filtering of pseudopotentials in real space calculations is proposed, in order to reduce the artifact of positional energy dependence ("egg box" effect). It is based on an improved version of the mask function method poposed by Wang [Phys. Rev. B 64, 201107/1 (2001)]. It is easy to implement, efficient, and accurate. By using atom-centered compensation charges, the local part of the pseudopotential becomes short ranged and can be filtered on the same footing as the nonlocal parts. A major advantage of the approach is that a generic set of parameters can be used for different pseudopotentials. A balanced parameter set is derived and validated. In this context a strategy to monitor the extent of grid dependence is introduced. It is found that, given a sufficiently fine grid spacing is used to represent the atomic valence density, the positional energy dependence can be reduced below 0.1 mhartree for all investigated atoms. On the example of a D(3h) symmetric Si(5) cluster and the C(60) molecule it is demonstrated that the artificial symmetry breaking of both bond lengths and orbital energies can substantially be reduced by the filtering scheme.