Study of Actinides by Relativistic Coupled Cluster Methods

This chapter addresses high-accuracy calculations of actinide systems. Lanthanide systems, where the broader availability of experimental data provides more extensive checks of computed properties, are discussed. The chapter presents predictions for the eka-actinide atoms E121 (eka-Ac) and E122 (eka-Th). Actinides (as well as their lanthanide homologues) present severe problems to theory and computations, caused by large, non-additive relativistic and correlation effects, further complicated by the multireference character of many electronic states, involving the 5f, 6d, 6p, and 7s orbitals. The chapter gives an overview of a state-of-the-art ab initio approach used in computational actinide chemistry and atomic physics: the relativistic Fock-space coupled cluster (RFSCC) method. The Fock-space and intermediate Hamiltonian coupled cluster methods were applied to the ground and excited levels of the second actinide element, thorium, and its heavy homologue eka-thorium.