Quasirelativistic energy-consistent 5f-in-core pseudopotentials for pentavalent and hexavalent actinide elements

Relativistic Pseudopotentials and Their Applications

“…In the case of the scalar-relativistic WB PPs, one distinguishes between f-in-valence SPPs [21,22] and f-in-core LPPs [7][8][9][10][11][12]. The LPPs include the open f shell in the PP core and thus avoid its difficult correlation treatment.…”

“…If the LPP and SPP 5f occupations obtained from Mulliken population analyses differ by less than 0.5 electrons, the application of the LPP should yield reasonable results. In the case of actinide fluorides, the 5f occupations differ by at most 0.1 electrons for AnF 2 /AnF 3 /AnF 4 (except for ThF 3 /PaF 3 , where the trivalent oxidation state is not preferred/unstable), 0.3 electrons for AnF 5 , and 0.9 electrons for AnF 6 [12], which explains the good results using the di-, tri-, and tetravalent, the acceptable results using the pentavalent, and the bad results using the hexavalent LPPs. Thus, the 5f-in-core approximation reaches its limit for the hexavalent oxidation state and therefore these LPPs should only be used to preoptimize structures.…”

“…Furthermore, ECPs permit the usage of smaller basis sets and thus the basis set superposition error is less significant compared to AE calculations. Even the difficulties due to open shells may be avoided by applying ECPs, if these open shells are included in the core system as it is the case for the 4f-in-core [7][8][9] and 5f-in-core [10][11][12] pseudopotentials (PP) for lanthanides and actinides, respectively. However, these PPs can only be applied, if the f orbitals do not participate significantly in chemical bonding (see Section 6.3.1).…”

“…Furthermore, ECPs are categorized by the size of their core, e.g., one differs between f-in-valence small-core [21,22] and f-in-core large-core PPs (LPP) [7][8][9][10][11][12] for the f elements. Finally, the accuracy of the underlying AE reference data determines the ECP type, e.g., for early actinides scalarrelativistic Wood-Boring (WB) [22] or relativistic multiconfiguration Dirac-Hartree-Fock (MCDHF) [23,24] small-core PPs (SPP) are available.…”

Efficient quantum chemical valence-only treatments of lanthanide and actinide systems

“…Although the 5f shell of the actinides is radially more extended than the 4f shell of the lanthanides and for the lighter actinides also actively participates in chemical bonding, it proved to be possible to derive 5f-in-core PPs for actinides with valencies ranging from two to six [49,50,51]. Their applications saves a significant amount of computer ressources with respect to an explicit treatment of the 5f shell, especially with respect to AE calculations.…”