Simulating X-ray Absorption Spectra with Linear-Response Density Cumulant Theory.

Area of Science:

• Computational Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Simulating X-ray absorption spectra is crucial for understanding molecular electronic structure.
• Existing methods may face challenges in efficiency or accuracy for core-excited states.

Purpose of the Study:

• To introduce and evaluate a new computational method, CVS-ODC-12, for simulating X-ray absorption spectra.
• To assess the performance of CVS-ODC-12 against experimental data and established computational techniques.

Main Methods:

• Utilizing linear-response density cumulant theory (LR-DCT) with the LR-ODC-12 formulation.
• Incorporating the core-valence separation (CVS) approximation for efficient computation of core-excited states.
• Benchmarking the CVS-ODC-12 method against experimental X-ray absorption spectra of small molecules.

Main Results:

• The CVS-ODC-12 method demonstrates good agreement with experimental data for transition intensities and relative energy spacings.
• Excitation energies calculated by CVS-ODC-12 are systematically overestimated compared to experimental values.
• The method's performance in terms of intensities and peak separations is comparable to excited-state coupled cluster methods.

Conclusions:

• CVS-ODC-12 provides an efficient and accurate approach for simulating X-ray absorption spectra, particularly for transition intensities and peak separations.
• The method's reliance on diagonalizing a Hermitian matrix facilitates efficient computation.
• Further refinements may be needed to address the systematic overestimation of excitation energies.