Basis-set extensions for two-component spin-orbit treatments of heavy elements

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Relativistic Effects

Background:

• Standard basis sets, typically quadruple-zeta or lower, are often used in two-component self-consistent field (SCF) calculations.
• These basis sets are usually optimized for scalar relativistic calculations and may not accurately capture effects like spin-orbit coupling.
• Spin-orbit coupling significantly impacts inner electron shells, causing energetic and spatial splittings.

Purpose of the Study:

• To investigate the accuracy of standard basis sets for two-component SCF calculations that include spin-orbit coupling.
• To evaluate the performance of these basis sets for heavy elements (In-I and Au-At).
• To propose and demonstrate a method for correcting errors arising from inadequate basis set description of spin-orbit coupling.

Main Methods:

• Investigated the accuracy of standard basis sets (quadruple-zeta and lower) in two-component SCF procedures.
• Focused on calculations including spin-orbit coupling for elements Indium (In) through Iodine (I) and Gold (Au) through Astatine (At).
• Proposed and tested the addition of a few steep basis functions to correct deficiencies.

Main Results:

• Standard basis sets show significant inaccuracies in describing spin-orbit coupling effects.
• These inaccuracies lead to large errors in total atomic energies and atomization energies of compounds containing heavy elements.
• The addition of a few steep basis functions effectively corrects these errors, yielding high-quality extended basis sets.

Conclusions:

• Standard basis sets are inadequate for accurate relativistic calculations involving spin-orbit coupling for heavy elements.
• A simple augmentation strategy by adding specific basis functions can significantly improve accuracy.
• The developed extended basis sets provide a reliable and accurate approach for relativistic quantum chemical calculations.