Reference Energies for Valence Ionizations and Satellite Transitions
Antoine Marie1, Pierre-François Loos1
1Laboratoire de Chimie et Physique Quantiques (UMR 5626), Université de Toulouse, CNRS, UPS, Toulouse 31062, France.
Journal of Chemical Theory and Computation
|May 22, 2024
Summary
This study introduces accurate computational methods for modeling "satellite" transitions in atomic and molecular ionization spectra. These methods provide reliable reference data for evaluating the performance of various quantum chemistry techniques.
Area of Science:
- Quantum Chemistry
- Computational Spectroscopy
- Theoretical Atomic and Molecular Physics
Background:
- Ionization can lead to simultaneous electron excitation, forming "satellite" or "shakeup" states.
- These satellite transitions, appearing as weaker, broader peaks in spectra, are challenging to model due to their high excitation degree.
- Accurate modeling of these states is crucial for understanding complex ionization processes.
Purpose of the Study:
- To compute highly accurate reference energies for satellite transitions and ionization potentials (IPs) in small molecules.
- To assess the accuracy of various quantum chemical methods, including coupled-cluster (CC) and many-body Green's function (MBGF) approaches, against these references.
- To identify the limitations of current computational methods in describing satellite transitions.
Main Methods:
- Utilized the Configuration Interaction using a Perturbative Selection made Iteratively (CIPSI) method to obtain full configuration interaction quality energies.
- Calculated 42 satellite transition energies and 58 valence ionization potentials (IPs).
- Evaluated the performance of coupled-cluster (CC2-CCSDTQ) and many-body Green's function (GW, GF2, T-matrix) approximations.
Main Results:
- Generated a benchmark dataset of accurate satellite transition energies and IPs for small molecular systems.
- Gauged the accuracy of various coupled-cluster methods against the high-quality reference data.
- Analyzed the performance of Green's function methods and discussed their limitations for satellite transitions.
Conclusions:
- The study provides essential reference data for validating theoretical models of ionization spectra.
- Highlights the challenges and limitations of commonly used computational methods in accurately describing satellite transitions.
- Offers insights into improving theoretical approaches for complex electronic excitation phenomena accompanying ionization.
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