Structure and spectroscopy of Pa4+ defects in Cs2ZrCl6. An ab initio theoretical study

In this paper we present the results of spin–orbit relativistic ab initio model potential embedded cluster calculations on (PaCl6)2− embedded in a reliable representation of the Cs2ZrCl6 host. Totally symmetric local distortions and vibrational frequencies are calculated for all the states of the 5f1 and 6d1 manifolds, as well as the corresponding 5f↔6d transition energies and the shape of the 5f(Γ8u)←6d(Γ8g) fluorescence band. An excellent overall agreement with available experimental data is observed which allows us to conclude that the quality of the spin–orbit operators used is very high for actinide elements, as was already known for transition metal and lanthanide elements. Furthermore, it is concluded that the structural and spectroscopic information produced here is very reliable and that the 6d(Γ8g′) state is around 10 000 cm−1 higher in energy than it was thought; our calculations suggest a value of 30 000 cm−1 for the 10Dq parameter of Pa4+ in Cs2ZrCl6, which would be compatible with the lower limit of 20 000 cm−1 accepted for Ce3+ in Cs2NaYCl6.