Multireference <i>ab initio</i> studies of magnetic properties of TbPc₂-type single-molecule magnets in different charge states

Lanthanide-based single-molecule magnets (SMMs) can have exceptionally large magnetic anisotropy due to interplay between the ligand crystal field and spin-orbit interaction. Among them, TbPc₂ SMM was shown to be promising for quantum information science applications. Although a variety of TbPc₂-type SMMs were synthesized in neutral and charged states under different chemical environment, there are no systematic theoretical studies of magnetic properties of such SMMs yet. Almost degenerate 4f orbitals demand multireference quantum chemistry calculations for the magnetic properties. Here, we investigate electronic structure and magnetic properties of TbPc₂ and TbPcNc SMMs as a function of oxidation state, ligand type and distortion of molecular geometry, using first-principles relativistic multireference methods including spin-orbit interaction. By applying effective pseudospin Hamiltonian to the lowest multiplet, we examine how these chemical factors affect several important energy scales, such as tunnel splitting, exchange coupling between the Tb magnetic moment and the ligand spin, zero-field splitting, and magnetic anisotropy barrier.