Linear Absorption Spectra from Explicitly Time-Dependent Equation-of-Motion Coupled-Cluster Theory

Area of Science:

• Quantum Chemistry
• Computational Spectroscopy
• Theoretical Molecular Physics

Background:

• Equation-of-motion coupled-cluster (EOM-CC) theory is a powerful method for electronic structure calculations.
• Conventional frequency-domain methods for linear absorption spectra can be computationally intensive for systems with high density of states.
• Time-dependent approaches in EOM-CC typically focus on wave function evolution.

Purpose of the Study:

• To develop and present an explicitly time-dependent approach for calculating linear absorption spectra.
• To introduce a novel formalism based on the time-evolution of a dipole function within EOM-CC theory.
• To provide a computationally tractable method for broad spectral ranges and complex molecular systems.

Main Methods:

• Developed an explicitly time-dependent EOM-CC formalism.
• Focused on the time-evolution of a dipole function, avoiding approximations.
• Implemented and validated the approach using EOM second-order approximate CC (CC2) and time-dependent EOM-CC2 (TD-EOM-CC2).

Main Results:

• The time-dependent dipole function formalism introduces no approximations.
• The method is suitable for molecules with a high density of states and broad spectral ranges.
• Validation against small molecules at CC2 and TD-EOM-CC2 levels showed good agreement.
• TD-EOM-CC2 predictions for extreme ultraviolet absorption spectra of third-row ions showed reasonable agreement with experimental data.

Conclusions:

• The explicitly time-dependent approach offers a robust and efficient alternative for calculating linear absorption spectra.
• This method overcomes limitations of conventional frequency-domain techniques for complex systems.
• The dipole function formalism provides a computationally advantageous route for spectroscopic predictions.