Relativistic nonorthogonal configuration interaction: application to L_2,3-edge X-ray spectroscopy

Area of Science:

• Quantum Chemistry
• Spectroscopy
• Computational Physics

Background:

• Calculating X-ray spectra requires accurate relativistic wave functions.
• Nonorthogonal Configuration Interaction (NOCI) has not been previously applied to relativistic wave functions.

Purpose of the Study:

• To develop and validate a relativistic exact-two-component nonorthogonal configuration interaction (X2C-NOCI) method for L-edge X-ray spectra.
• To assess the accuracy and computational scaling of the new method.

Main Methods:

• Development of the relativistic exact-two-component nonorthogonal configuration interaction (X2C-NOCI) method.
• Application to molecular complexes (SF₆, SiCl₄, [FeCl₆]^3-).
• Implementation of improved integral screening for computational efficiency.

Main Results:

• X2C-NOCI successfully captures key features of L_2,3-edge X-ray absorption spectra.
• The method allows for explicit treatment of orbital optimization, crucial for core excitations.
• Demonstrated accuracy and computational scaling for tested molecular systems.

Conclusions:

• X2C-NOCI is a promising method for relativistic L-edge X-ray spectra.
• The proposed integral screening enhances computational feasibility.
• This work represents the first application of NOCI to relativistic wave functions.