Time-Dependent Relativistic Two-Component Equation-of-Motion Coupled Cluster for Open-Shell Systems: TD-EA/IP-EOMCC
P D Varuna S Pathirage1, Stephen H Yuwono1, Xiaosong Li2
1Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, United States.
The Journal of Physical Chemistry. A
|June 18, 2026
Summary
This study introduces a new computational method combining imaginary-time and real-time simulations to accurately calculate linear absorption spectra for open-shell systems using electron attachment (EA) and ionization potential (IP) equation-of-motion coupled-cluster (EOMCC) theory.
Area of Science:
- Quantum Chemistry
- Computational Spectroscopy
- Relativistic Quantum Mechanics
Background:
- Calculating linear absorption spectra for open-shell systems is computationally demanding.
- Existing methods often rely on frequency-domain calculations, which can be limited.
- Accurate spectral data is crucial for understanding electronic transitions in various chemical species.
Purpose of the Study:
- To develop and validate a combined imaginary-time/real-time time-dependent approach for linear absorption spectra.
- To apply this method to electron attachment (EA) and ionization potential (IP) equation-of-motion coupled-cluster (EOMCC) calculations.
- To evaluate the method's accuracy within the exact two-component relativistic framework.
Main Methods:
- A novel combined imaginary-time and real-time time-dependent (TD) simulation approach.
- Utilizing electron attachment (EA) and ionization potential (IP) equation-of-motion coupled-cluster (EOMCC) theory.
- Employing the exact two-component relativistic framework for calculations.
Main Results:
- The TD-EA/IP-EOMCC method accurately reproduces linear absorption spectra for open-shell atoms and diatomics.
- Results closely match those from standard frequency-domain TD-EA/IP calculations.
- The overlap of low-lying states with the Koopmans determinant influences the required simulation time.
Conclusions:
- The combined imaginary-time/real-time TD-EA/IP-EOMCC approach is a viable and accurate method for spectral calculations.
- This method offers a robust alternative for studying open-shell systems.
- Understanding initial state properties is key for accurate spectral simulations.
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