To address ultimate precision in density-functional-theory calculations we employ the full-potential linearized augmented planewave + local-orbital (LAPW+lo) method and justify its usage as a benchmark method. LAPW+lo and two completely unrelated numerical approaches, multi-resolution analysis (MRA) and linear combination of atomic orbitals, yield total energies of atoms with a mean deviation of 0.9~{\mu}Ha and 0.2~{\mu}Ha, respectively. Spectacular agreement with the MRA is reached also for total and atomization energies of the G2-1 set consisting of 55 molecules. With the example of α-iron we demonstrate the capability of LAPW+lo of reaching {\mu}Ha/atom precision also for periodic systems, which allows also for distinction between numerical precision and the accuracy of a given functional.
@article{arxiv.1803.00776,
title = {Microhartree Precision in Density-Functional-Theory Calculations},
author = {Andris Gulans and Anton Kozhevnikov and Claudia Draxl},
journal= {arXiv preprint arXiv:1803.00776},
year = {2018}
}