On the accuracy of one-component pseudopotential spin-orbit calculations

Area of Science:

• Quantum Chemistry
• Computational Physics

Background:

• Spin-orbit coupling (SOC) is crucial for accurate electronic structure calculations.
• Current one-component pseudopotential methods can overcount SOC effects, leading to inaccuracies.
• Valence spin-orbit polarization and relaxation effects are often implicitly included in pseudopotentials.

Purpose of the Study:

• To investigate improvements in one-component extraction procedures for spin-orbit pseudopotentials.
• To address the issue of double-counting spin-orbit effects in high-accuracy computations.
• To develop and validate new methods for extracting spin-orbit pseudopotentials.

Main Methods:

• Perturbation-theory formalism was used to analyze pseudopotential extraction.
• An "explicit" method involving four-component spin-orbit CI was investigated.
• An "implicit" method using single-excitation spin-orbit CI was developed and tested.

Main Results:

• One-component pseudopotentials extracted at the SCF level include valence SOC effects.
• Using these pseudopotentials in standard CI methods leads to double counting.
• The "explicit" method proved cumbersome due to nonadditivity and pseudovariational collapse.
• The "implicit" method successfully resolved the double-counting problem in atomic tests on iodine.

Conclusions:

• The "implicit" method offers an accurate and efficient way to extract spin-orbit pseudopotentials.
• This advancement is vital for high-accuracy spin-orbit coupling energy computations.
• The developed method overcomes limitations of previous approaches, enabling more reliable calculations.