LAUSR

We present a computationally efficient approach to perform systematically convergent real-space all-electron Kohn-Sham DFT calculations for solids using an enriched finite element (FE) basis. The enriched FE basis is constructed by augmenting the classical FE basis with atom-centered numerical basis functions, comprising of atomic solutions to the Kohn-Sham problem. Notably, to improve the conditioning we orthogonalize the enrichment functions with respect to the classical FE basis, without sacrificing the locality of the resultant basis. In addition to improved conditioning, this orthogonalization procedure also renders the overlap matrix block-diagonal, greatly simplifying its inversion. Subsequently, we use a Chebyshev polynomial based filtering technique to efficiently compute the occupied eigenspace in each self-consistent field iteration. We demonstrate the accuracy and efficiency of the proposed approach on periodic unit-cells and supercells, ranging up to $\sim10,000$ electrons. The benchmark studies considered show a staggering $130\times$ speedup of the orthogonalized enriched FE basis over the classical FE basis. We also demonstrate that the orthogonalized enriched FE basis outperforms the LAPW+lo basis in terms of computational efficiency for and beyond modest sized systems. Finally, we observe good parallel scalability of our implementation with $95\%$ efficiency at $24\times$ speedup for a system with 620 electrons.