Improved Segmented All-Electron Relativistically Contracted Basis Sets for the Lanthanides

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Atomic Physics

Background:

• Segmented all-electron relativistically contracted (SARC) basis sets are crucial for accurate electronic structure calculations of heavy elements.
• Existing SARC basis sets, while efficient, require further optimization for advanced quantum chemical methods, particularly for lanthanides.

Purpose of the Study:

• To introduce the second-generation SARC2 basis sets for lanthanides, enhancing computational accuracy.
• To adapt these basis sets for use with both Density Functional Theory (DFT) and wave function-based methods.
• To improve the prediction of spin-orbit coupling (SOC) parameters and other electronic properties.

Main Methods:

• Development of SARC2 basis sets with optimized exponents via a new orbital shape fitting procedure.
• Expansion of the f-orbital space and inclusion of new polarization/correlation functions.
• Creation of auxiliary basis sets for resolution-of-identity (RI) approximations in DFT and wave function calculations.

Main Results:

• SARC2 basis sets show significant improvements in Complete Active Space Self-Consistent Field (CASSCF) energies.
• More accurate prediction of spin-orbit coupling parameters for lanthanide systems.
• Benchmarking confirms suitability for excitation energies, geometries, ionization potentials, and radial distributions.

Conclusions:

• The SARC2 basis sets extend the utility of previous DFT-focused sets to routine all-electron wave function treatments of lanthanide complexes.
• These new basis sets are well-suited for studying magnetic and spectroscopic properties of lanthanides using both DFT and multireference methods.
• The enhanced accuracy facilitates more reliable computational studies in chemistry and physics involving lanthanides.