Computing x-ray absorption spectra from linear-response particles atop optimized holes.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• State-specific orbital optimized density functional theory (OO-DFT) methods, like restricted open-shell Kohn-Sham (ROKS), offer semiquantitative accuracy for predicting x-ray absorption spectra.
• A key limitation of OO-DFT methods is the necessity for individual state optimization, which is computationally intensive.

Purpose of the Study:

• To develop an efficient approach for predicting x-ray absorption spectra.
• To introduce a method that bypasses the need for state-specific optimization in OO-DFT calculations.
• To provide a computationally less expensive alternative for obtaining accurate spectra.

Main Methods:

• A hybrid approach combining core-hole optimization through the core-ionized state with electron-addition configuration interaction singles (CIS) was developed.
• This method, termed ROKS(STEX), generalizes the static-exchange (STEX) method within a DFT framework.
• Local functionals like PBE and OLYP were employed for calculations.

Main Results:

• The ROKS(STEX) approach achieved an approximate root-mean-square (rms) error of ~0.6 eV for K-edges of C-F compounds.
• The method demonstrated reasonable accuracy without requiring state-specific optimizations.
• It was shown to be effective in identifying key transitions for subsequent full OO ROKS treatment.

Conclusions:

• The ROKS(STEX) method offers an efficient and accurate technique for predicting x-ray absorption spectra.
• This approach significantly reduces the computational cost associated with obtaining OO-DFT quality spectra.
• ROKS(STEX) is a valuable tool for the rapid and reliable prediction of x-ray absorption spectra.