Nature of hyperfine interactions in TbPc₂ single-molecule magnets: Multireference <i>ab-initio</i> study

Lanthanide-based single-ion magnetic molecules can have large magnetic hyperfine interactions as well as large magnetic anisotropy. Recent experimental studies reported the tunability of these properties by changes of chemical environments or by application of external stimuli for device applications. In order to provide insight into the origin and mechanism of such tunability, here we investigate the magnetic hyperfine and nuclear quadrupole interactions of TbPc₂ single-molecule magnets using first-principles multireference methods including spin-orbit interaction. The microscopic Hamiltonian is mapped onto an effective Hamiltonian with an electronic pseudo-spin S=1/2. We discuss the physical origin of ab-initio-calculated hyperfine interaction parameters and their dependence on the experimental molecular geometry and structure distortions. We show the ab-initio-calculated electronic-nuclear spectrum and compare it with experimental data. We further analyze the role of the non-axial quadrupole interactions in the formation of avoided level crossings and magnetization dynamics.