Multireference Approach to Normal and Resonant Auger Spectra Based on the One-Center Approximation

Area of Science:

• Quantum Chemistry
• Atomic and Molecular Physics
• Computational Spectroscopy

Background:

• Calculating Auger decay rates is crucial for understanding atomic and molecular ionization processes.
• Existing methods for ionization and autoionization can be complex and difficult for non-experts.
• The One-Center Approximation (OCA) offers a potential simplification.

Purpose of the Study:

• To implement and validate a new methodology for calculating normal and resonant Auger decay rates.
• To simplify the computation of Auger decay rates by integrating it within existing quantum chemistry frameworks.
• To provide an accessible tool for studying ionization and autoionization phenomena.

Main Methods:

• Utilized the One-Center Approximation (OCA) with atomic radial Auger integrals.
• Implemented within restricted-active-space self-consistent-field (RASSCF) and multistate restricted-active-space perturbation theory of second order (MS-RASPT2) frameworks.
• Optimized wave functions independently for initial and final states, using state-interaction (SI) approach for Auger matrix elements.

Main Results:

• Successfully implemented a methodology to calculate Auger decay rates directly within OpenMolcas.
• Avoided the need for external programs by projecting intensities onto the atomic center with the core hole.
• Validated the approach on the Ne atom and several prototype molecules (CO, N2, HNCO, H2O, NO2, pyrimidine).

Conclusions:

• The developed methodology offers a simplified and integrated approach to calculating Auger decay rates.
• This method enhances accessibility for studying complex ionization and autoionization processes.
• The successful validation demonstrates the robustness and applicability of the implemented approach.