Relativistic Four-Component Multireference Coupled Cluster Methods: Towards A Covariant Approach

Study of Actinides by Relativistic Coupled Cluster Methods

“…Comprehensive methodological discussions appear in our 2010 reviews [6,7]. Only brief descriptions will be given in this section.…”

“…Multireference variants of relativistic 4-component CC methods capable of handling quasidegeneracies, which are important for open-shell heavy atomic and molecular systems, have been developed in recent years [15, 17-19, 21, 31]. In particular, the multireference FSCC scheme [32,33] is applicable to systems with a variable number of particles, and is an ideal candidate for merging with QED theory to create an infinite-order size-extensive covariant many-body method applicable to systems with variable numbers of fermions and bosons [6,7].…”

“…This outstanding capability of the FSCC method is a consequence of its "valence universality," the applicability of the method to systems with different numbers of particles (a fundamental feature of QED systems). A pilot variant of RFSCC, called double FSCC (DFSCC), has been proposed recently [6,7]. The DFSCC is derived directly from QED, using the Lagrangian formalism and covariant evolution operator (CEO) of Lindgren [8].…”

“…This approach includes the treatment of both electronic and photonic degrees of freedom on equal quantum footing. DFSCC yields a possible avenue for covariant treatment of heavy relativistic multielectronic systems with high precision (see [6,7]). It is still under development, and will not be discussed here.…”

“…The RFSCC approach is computationally demanding, limiting its scope to actinide atoms and small molecules. For recent, more general reviews of RFSCC and its applications to other heavy and superheavy systems, refer to Eliav and Kaldor [6,7].…”