Exact semi-classical light-matter interaction operator applied to two-photon processes with strong relativistic...

Area of Science:

• Atomic and Molecular Physics
• Computational Chemistry
• X-ray Spectroscopy

Background:

• X-ray interactions necessitate moving beyond the electric-dipole approximation due to short wavelengths.
• The exact semi-classical light-matter interaction operator provides advantages over multipole expansion.
• Modeling X-ray scattering in metal K pre-edges involves relativistic two-photon processes with electric-dipole forbidden transitions.

Purpose of the Study:

• To develop and implement an efficient computational method for modeling X-ray scattering processes.
• To address the computational bottleneck in calculating integrals for numerous transitions.
• To accurately model K-edge X-ray scattering in systems relevant to heme enzyme studies.

Main Methods:

• Utilized the exact semi-classical light-matter interaction operator.
• Employed the restricted active space state-interaction approach for multiconfigurational wavefunctions.
• Developed a novel integral calculation scheme within the molecular-orbital basis and a grouping strategy to accelerate computations.

Main Results:

• The new computational scheme significantly reduces the time required for X-ray scattering calculations by several orders of magnitude.
• The method enables accurate spectral calculations for complex systems, including those with multiconfigurational wavefunctions.
• Transition intensities were affected by 0.1% or less, demonstrating the accuracy of the accelerated method.

Conclusions:

• The developed computational approach offers a substantial speed-up for modeling X-ray scattering, particularly for two-photon processes.
• This advancement is critical for the study of systems like iron-porphyrin complexes and has implications for heme enzyme research.
• The improved efficiency allows for more feasible and accurate investigations in X-ray spectroscopy.