Calculating vibrational excitation energies using tensor-decomposed vibrational coupled-cluster response theory

Area of Science:

• Quantum Chemistry
• Computational Spectroscopy
• Molecular Physics

Background:

• Vibrational coupled cluster (VCC) theory is a powerful method for calculating molecular vibrational properties.
• Previous VCC implementations required significant computational resources due to large tensor constructions.
• Calculating vibrational excitation energies is crucial for understanding molecular behavior and spectra.

Purpose of the Study:

• To implement and present the first application of tensor-decomposed vibrational coupled cluster (CP-VCC) response theory.
• To develop an efficient method for calculating vibrational excitation energies.
• To demonstrate the applicability of CP-VCC for molecules of increasing complexity.

Main Methods:

• Generalization of the CP-VCC algorithm to incorporate Jacobian matrix transformations for response theory.
• Development of a novel eigenvalue solver for CP-VCC excitation energy computations.
• Systematic investigation of numerical thresholds for controlling accuracy and enabling black-box calculations.

Main Results:

• Successful calculation of the 20 lowest vibrational excitation energies for 10 four-atomic molecules.
• Efficient computation of vibrational eigenstates for polycyclic aromatic hydrocarbons (PAHs) up to PAH8 (120 modes).
• Demonstration that tensor decomposition errors can be controlled via numerical thresholds, ensuring accuracy.

Conclusions:

• The tensor-decomposed VCC response theory provides an efficient and accurate approach for calculating vibrational excitation energies.
• The method significantly reduces memory and computational time compared to traditional full-tensor approaches.
• The developed black-box approach simplifies calculations, requiring minimal user input for high-quality results.