Ultrafast Near-Edge X-ray Absorption Fine Structure Calculations with the Exact Integral Simplified Time-Dependent...

Area of Science:

• Quantum chemistry
• Spectroscopy
• Computational physics

Background:

• Calculating near-edge X-ray absorption fine structure (NEXAFS) is computationally demanding for large systems due to the high density of core-valence excited states.
• Existing quantum chemistry (QC) methods struggle with the accuracy and speed required for complex molecular systems.

Purpose of the Study:

• To develop an ultrafast and accurate computational method for NEXAFS spectra.
• To enable the study of core-valence excited states in medium to large molecular systems.
• To validate the proposed method by comparing computed spectra with experimental data.

Main Methods:

• Implementation of an ultrafast method based on the exact integral simplified time-dependent density functional theory (XsTD-DFT) framework.
• Utilizing short-range corrected exchange-correlation functionals with the Tamm-Dancoff approximation.
• Computation of oxygen K-edge NEXAFS spectrum for a 600-atom collagen model.

Main Results:

• The method achieved computations in under a minute for small to medium systems, showing excellent agreement with experimental results.
• Accurate reproduction of the experimental oxygen K-edge NEXAFS spectrum for a collagen model was achieved by computing 85,672 1s_O core-valence excited states.
• The calculation for the collagen model, involving a significant number of excited states, was completed in 11 days on a desktop computer.

Conclusions:

• The proposed ultrafast method provides an accurate and efficient approach for computing NEXAFS spectra.
• The method demonstrates excellent performance even for relatively large molecular models like collagen.
• This advancement pushes the boundaries of quantum chemistry in analyzing complex spectroscopic data.