As the relativistic corrections become stronger for late-row elements, the fully perturbative treatment of spin-orbit coupling and dynamic correlation may become inadequate for accurate descriptions of chemical properties. In this talk, I will discuss the development of variational relativistic multiference methods, including CASSCF, MRCI, MRPT2, and MCPDFT. Benchmark studies of atomic fine structure splitting show that variational approaches outperforms the fully perturbative CASPT2-SO for heavier atomic species (&gt;4th row). This observation suggests that as the strength of the spin-orbit coupling increases, the coupling between relativistic corrections and dynamic correlation also increases and cannot be treated as separate perturbations. I will also discuss how the correlation space affect various heavy element properties.

Variational relativistic multireference methods for heavy-element chemistry

ACS Spring 2022

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