The ab initio model potential embedded cluster method (AIMP) was applied to the calculation fo the U-Cl equilibrium distances, totally symmetric vibrational frequencies, and 5f2→5f2, 5f2→5f16d1 electronic transitions of the octahedral (UCl6)2- defect cluster in the Cs2ZrCl6 host crystal. As such, the Cs2ZrCl6 AIMP embedding potential produced in previous works incorporates quantum-mechanical host effects. These effects were incorporated in a final set of spin-orbit configuration interaction (CI) calculations by means of the spin-free state shifted (sfss) Wood-Boring AIMP Hamiltonian.