(J)over-tilde-pseudospin states and the crystal field of cubic systems

The theory of (J) over tilde pseudospin for the f element in a cubic environment is developed. By fulfilling the symmetry requirements and the adiabatic connection to the atomic limit, the crystal-field states are uniquely transformed into (J) over tilde -pseudospin states. In terms of the pseudospin operators, both the total angular momentum and the crystal-field Hamiltonian contain higher-rank tensor terms than the traditional ones do, which means the present framework naturally includes effects such as covalency and J mixing beyond the f -shell model. Combining the developed theory with ab initio calculations, the (J) over tilde -pseudospin states for Nd3+ and Np4+ ions in octahedral sites of insulators are derived.