An efficient first principles method for molecular pump-probe NEXAFS spectra: Application to thymine and azobenzene

Area of Science:

• Quantum chemistry
• Spectroscopy
• Computational physics

Background:

• Pump-probe near edge X-ray absorption fine structure (PP-NEXAFS) spectroscopy probes valence-excited states in molecules.
• Existing computational methods for PP-NEXAFS are computationally expensive and not suitable for large molecules.

Purpose of the Study:

• To develop an efficient, first-principles computational method for calculating molecular ground state and PP-NEXAFS spectra.
• To enable accurate calculations for medium-sized and large molecules.

Main Methods:

• Density functional theory (DFT) combined with transition potential (TP) and Δ self-consistent field (ΔSCF) methodologies.
• Application to n → π* pump/O-K-edge NEXAFS of thymine.
• Application to n → π* and π → π* pump/N-K-edge NEXAFS of azobenzene isomers.

Main Results:

• The proposed TP-DFT/ΔSCF method efficiently computes molecular ground state and PP-NEXAFS spectra.
• The method provides accurate spectral predictions for studied molecules.
• Demonstrated applicability to thymine and azobenzene systems.

Conclusions:

• The TP-DFT/ΔSCF method offers a computationally feasible approach for PP-NEXAFS calculations.
• This method expands the scope of theoretical investigations for excited-state molecular properties.
• Facilitates the study of optically dark states in various molecular systems.