Communication: X-ray absorption spectra and core-ionization potentials within a core-valence separated coupled...

Area of Science:

• Computational chemistry
• Quantum chemistry
• Spectroscopy

Background:

• Coupled cluster linear response theory is a powerful tool for calculating electronic excitation energies.
• Calculating core ionization energies and X-ray absorption spectra requires accurate treatment of electron correlation.
• Existing methods can be computationally expensive, especially for larger systems.

Purpose of the Study:

• To present a simplified scheme for computing X-ray absorption spectra and core ionization energies.
• To reduce the computational cost associated with these calculations within coupled cluster linear response theory.
• To develop and validate a perturbation correction for improved accuracy.

Main Methods:

• Exploiting core-valence separation to reduce the excitation space.
• Implementing the scheme within existing coupled cluster codes.
• Developing a perturbation correction for the excluded excitation space.
• Testing the method on molecular systems.

Main Results:

• The proposed scheme effectively computes X-ray absorption spectra and core ionization energies.
• The method significantly reduces the required excitation space.
• The perturbation correction enhances accuracy.
• Accurate results were obtained for molecular systems, comparable to full-space calculations.

Conclusions:

• The presented scheme offers a computationally efficient and accurate approach for calculating X-ray absorption spectra and core ionization energies.
• The method is readily implementable in standard coupled cluster codes.
• The approach is generalizable to various levels of coupled cluster theory, including CC3.