Relativistic small-core pseudopotentials for actinium, thorium, and protactinium

Area of Science:

• Computational Chemistry
• Relativistic Quantum Chemistry
• Atomic Physics

Background:

• Accurate theoretical descriptions of heavy elements, especially actinides, are crucial for understanding their chemical and physical properties.
• Small-core pseudopotentials significantly reduce computational cost for relativistic calculations.
• Previous work established pseudopotentials for uranium, necessitating similar tools for adjacent actinides.

Purpose of the Study:

• To develop and validate small-core pseudopotentials and accompanying basis sets for actinium (Ac), thorium (Th), and protactinium (Pa).
• To assess the accuracy of these pseudopotentials for calculating ionization potentials of these elements.
• To provide reliable computational tools for future studies of actinide chemistry.

Main Methods:

• Energy adjustment of small-core pseudopotentials to multiconfiguration Dirac-Hartree-Fock (MCDHF) reference data.
• Utilized the Dirac-Coulomb-Breit Hamiltonian and the Fermi nucleus model for relativistic effects.
• Calculated ionization potentials using Hartree-Fock (HF), multireference averaged coupled-pair functional (MR-ACPF), and Fock-space coupled cluster (FS-CC) methods.

Main Results:

• Optimized valence basis sets of polarized valence quadruple-ζ quality were developed.
• Atomic test calculations for the first four ionization potentials showed satisfactory agreement with HF and MR-ACPF levels.
• Highly correlated FS-CC calculations demonstrated excellent agreement between pseudopotential results and all-electron calculations/experimental data.

Conclusions:

• The developed pseudopotentials and basis sets for Ac, Th, and Pa are accurate and reliable for atomic calculations.
• These computational tools provide a significant improvement for studying the electronic structure of light actinides.
• The new sets supplement existing pseudopotentials for uranium, enabling comprehensive theoretical investigations across the early actinide series.