Quantities that underwent FFT-processing on a double grid suffer from a small amount of ringing artifacts with a period of the original (single) grid spacing. While the magnitude of the ringing is small, we are investigating sums of two components to the electric field (Hartree and pseudopotential) that have opposite signs and similar magnitudes, thus cancelling out to a large degree. This magnifies relative errors in the total electric field. To improve the accuracy of the calculated fields we smoothed the field values on the grid using a 27-point 3D stencil, where the stencil weights were given by B C 2 EF G , where 𝑑 B is the taxicab distance of a stencil point from the middle of the stencil. This procedure was found to efficiently attenuate the ringing artifacts.