[en] First-principles fully relativistic analysis of dependence of the 5d orbitals splitting (10Dq) and several types of electron transitions (including 4f-6s transition and several types of 'ligand-impurity ion' charge transfer (CT) transition) energies on the interionic distance has been performed for all trivalent lanthanides in Cs₂NaYCl₆ crystal. Salient feature of the method is that the four-component molecular orbitals (MO) composed of atomic wave functions are used in the calculations; this allows for a direct consideration of the covalent effects. Without introducing any fitting parameter, the power dependencies for 10Dq and linear dependencies for all considered electron transitions energies on the distance between the rare earth (RE) ions and ligands were obtained. The 10Dq parameter was shown to depend on distance as 1/Rⁿ, n ≠ 5 for all considered systems. Consideration of the calculated results revealed several trends based on the RE³⁺ atomic number and MO diagram for all RE³⁺ in Cs₂NaYCl₆. Obtained results can be used for analysis of the lattice relaxation effects and pressure dependence of the absorption spectra of RE³⁺-doped chloride crystals