Efficient Variable-Time Implementation of the RT-EOM-CCSDT Approach for Core and Valence Ionization Spectral...

Area of Science:

• Quantum Chemistry
• Computational Spectroscopy
• Molecular Physics

Background:

• The real-time equation-of-motion coupled cluster (RT-EOM-CC) method accurately predicts photoelectron spectral functions.
• Previous implementations included single and double excitations, with limitations for certain molecular systems.

Purpose of the Study:

• To extend the RT-EOM-CC method to include full triple excitations.
• To improve computational efficiency through an advanced time-integrator with a variable time step and improved solver.
• To validate the enhanced method by computing the photoelectron spectra of the water molecule.

Main Methods:

• Implementation of full triple excitations within the RT-EOM-CC framework.
• Development of an efficient time-integrator featuring a variable time step and an improved recursive equation solver.
• Application of the enhanced RT-EOM-CC method to calculate core and inner valence photoelectron spectra of water.

Main Results:

• The new RT-EOM-CC method with triple excitations (RT-EOM-CCSDT) shows excellent agreement with full configuration interaction results for the water molecule in a reduced active space.
• In a full active space, the inclusion of triple excitations successfully resolves discrepancies observed at the RT-EOM-CCSD level for water's photoelectron spectra.
• The computational efficiency is enhanced by the optimized time-integrator.

Conclusions:

• The inclusion of triple excitations in RT-EOM-CC significantly improves the accuracy of photoelectron spectral predictions, particularly for core and inner valence regions.
• The developed efficient time-integrator makes the computationally demanding triple excitations more feasible.
• This enhanced method provides a more accurate theoretical tool for studying molecular electronic structures and dynamics through photoelectron spectroscopy.