Teoría de Funcionales de Par-Densidad Linealizada con Acoplamiento Espín-Órbita

We include spin-orbit coupling (SOC) effects in linearized pair-density functional theory (L-PDFT), which is a multistate extension of multiconfiguration pair-density functional theory (MC-PDFT). Both 1-electron and 2-electron SOC integrals are computed using Breit-Pauli and Douglas-Kroll-Hess Hamiltonians in the atomic mean-field approximation. SO-L-PDFT removes the unphysical J-symmetry breaking observed in MC-PDFT. The accuracy of SO-L-PDFT is validated by calculations of zero-field splittings, fine-structure excitation energies, and low-energy excited-state spectra for a diverse group of atoms and molecules spanning the whole range of the periodic table, including atoms of groups 3, 11, and 13-17, the Ce³⁺ and U⁵⁺ ions, group 16 monohydrides, group 17 monoxides, lanthanide hexachlorides (${\left[{CeCl}_6\right]}^{3-}$, ${\left[{PrCl}_6\right]}^{3-}$, and ${\left[{NdCl}_6\right]}^{3-}$), actinyl ions (${\left[{UO}_2\right]}^{+}$, ${\left[{NpO}_2\right]}^{2+}$), and tricarbonatoactinyl complexes (${\left[{UO}_2{\left({CO}_3\right)}_3\right]}^{5-}$, ${\left[{NpO}_2{\left({CO}_3\right)}_3\right]}^{4-}$). We also compare the results to new spin-orbit-inclusive calculations by single-state and multistate multireference perturbation theory.