The real-space pseudopotential approach is a well-known
method
for large-scale density functional theory (DFT) calculations. One
of its main limitations, however, is the introduction of errors associated
with the positioning of the underlying real-space grid, a phenomenon
usually known as the “egg-box” effect. The effect can
be controlled by using a finer grid, but this raises the cost of the
calculations or even undermines their feasibility altogether. Therefore,
there is ongoing interest in the reduction of the effect per a given
real-space grid. Here, we present a finite difference interpolation
of electron orbitals as a means of exploiting the high resolution
of the pseudopotential to reduce egg-box effects systematically. We
implement the method in PARSEC, a finite difference real-space pseudopotential
DFT code, and demonstrate error mitigation and improved convergence
at a low additional computational cost.