This study focuses on investigating the intramolecular magnetic interaction in the excited state of rare-earth-based molecular magnets and proposing a new approach to manipulate their quantum states. The research employs GAUSSIAN, OpenMOLCAS, and ORCA software packages for various calculations, including density functional theory and relativistic ab initio wave function calculations. These calculations are utilized to optimize molecular geometries and determine the interaction between the lanthanide ion’s total angular momentum (J) and the ligand’s orbital angular momentum (L). So far, the results obtained reveal the ground multiplet states of the terbium complex using CASSCF calculations, indicating that the additional two occupied pi  orbitals and four unoccupied pi orbitals to the active space in the calculations does not significantly affect the energy gap between the two lowest substates in the ground state. This valuable information forms the fundamental basis for determining the J-L interaction.