HYPERION: A New Computational Tool for Relativistic Ab Initio Hyperfine Coupling

Herein we describe HYPERION, a new program for computing relativistic picture-change-corrected magnetic reso-nance parameters from scalar relativistic active space wave functions, with or without spin-orbit coupling (SOC) included a posteriori. HYPERION also includes a new orbital decomposition method for assisting active space selection for calculations of hyperfine coupling. For benchmarking purposes, we determine hyperfine coupling constants of selected alkali metal, transition metal, and lanthanide atoms, based on complete active space self-consistent field spin-orbit calculations in OpenMolcas. Our results are in excellent agreement with experimental data from atomic spectroscopy as well as theoretical predictions from four-component relativistic calculations.