Two approaches for improving the description of highly correlated 4f states in lanthanides, which are often overly delocalized and their energies are unreliable within standard Density Functional Theory (DFT). The first approach involves transforming the DFT electronic structure (obtained in Wien2k) into Wannier functions (Wannier90), that are localized on an atom, enabling direct evaluation of Crystal Field Parameters (CFP). The second approach focuses on determining the effective Hubbard parameter U (in Wien2k), a local correlation potential that is usually being considered as an adjustable parameter. Its assessment from DFT is shown on a well-studied material Ce-doped Y3Al5O12 garnet (YAG). The results are compared with standard spin-orbit GGA+U calculation performed in MedeA-VASP. All these characteristics are essential not only for modeling optical properties of rare earths ions embedded as impurities in oxide matrices that can be used for foton energy conversion, but also for an effective quantum mechanical description of highly correlated electron systems frequently applied in photo-electrocatalysis, chemical energy storage and conversion.