Finite Difference Interpolation for Reduction of Grid-Related Errors in Real-Space Pseudopotential Density Functional Theory

The real-space pseudopotential approach is a well-knownmethodfor large-scale density functional theory (DFT) calculations. Oneof its main limitations, however, is the introduction of errors associatedwith the positioning of the underlying real-space grid, a phenomenonusually known as the "egg-box" effect. The effect canbe controlled by using a finer grid, but this raises the cost of thecalculations or even undermines their feasibility altogether. Therefore,there is ongoing interest in the reduction of the effect per a givenreal-space grid. Here, we present a finite difference interpolationof electron orbitals as a means of exploiting the high resolutionof the pseudopotential to reduce egg-box effects systematically. Weimplement the method in PARSEC, a finite difference real-space pseudopotentialDFT code, and demonstrate error mitigation and improved convergenceat a low additional computational cost.