Quadratic response functions in the relativistic four-component Kohn-Sham approximation

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Accurate calculation of molecular optical properties is crucial for understanding material behavior.
• Relativistic effects and electron correlation significantly influence these properties, especially in heavy elements.
• Existing theoretical frameworks require refinement to incorporate these complex interactions comprehensively.

Purpose of the Study:

• To formulate and implement the quadratic response function within the adiabatic four-component Kohn-Sham approximation.
• To investigate the impact of relativistic effects and electron correlation on optical properties.
• To evaluate the performance of different functionals, specifically CAM-B3LYP and B3LYP, for these calculations.

Main Methods:

• Developed a quadratic response function for the adiabatic four-component Kohn-Sham (KSS) approximation.
• Utilized time-reversal symmetric Kramers pair spinors for the noninteracting reference state.
• Employed gradient correction for the energy density and performed calculations on disubstituted halobenzenes.

Main Results:

• Demonstrated that relativistic and correlation effects are not additive in influencing optical properties.
• Quantified the significant reduction in mubeta-response for bromobenzenes (62-75%) and enhancement for iodobenzenes (17-21%) due to relativity.
• Identified CAM-B3LYP as the best-performing functional, yielding hyperpolarizabilities distinct from B3LYP.

Conclusions:

• The implemented four-component KSS approach accurately captures significant relativistic effects on optical properties.
• Relativistic effects play a crucial role and cannot be simply added to correlation effects.
• CAM-B3LYP functional is recommended for accurate prediction of molecular hyperpolarizabilities in relativistic systems.