Efficient time-dependent vibrational coupled cluster computations with time-dependent basis sets at the two-mode...

Area of Science:

• Quantum Chemistry
• Molecular Dynamics
• Computational Spectroscopy

Background:

• Calculating molecular quantum dynamics is computationally demanding, requiring methods that balance accuracy and efficiency.
• Time-dependent variational-based vibrational coupled cluster theory (TDMVCC) has emerged as a promising approach for these calculations.
• Previous implementations demonstrated good accuracy but lacked computational efficiency for larger systems.

Purpose of the Study:

• To develop and implement an efficient version of TDMVCC capable of handling systems with up to two-mode couplings.
• To investigate strategies for reducing computational scaling, including the use of restricted active bases and hybrid approaches.
• To assess the performance and convergence of the new implementation for realistic molecular systems.

Main Methods:

• An efficient implementation of TDMVCC was developed, focusing on regrouping terms to achieve cubic computational scaling with the number of degrees of freedom.
• The study explored the use of restricted active one-mode basis functions and two specific limits: a full active basis and a hybrid TDMVCC/time-dependent Hartree (TDH) approach.
• Computational scaling was analyzed for polyaromatic hydrocarbons with up to 264 modes, and convergence was studied for the internal vibrational redistribution of benzoic acid.

Main Results:

• The efficient TDMVCC implementation achieves cubic scaling, significantly improving computational efficiency.
• The hybrid TDMVCC/TDH approach offers even lower computational scaling.
• Computations on benzoic acid demonstrated faster convergence of the hybrid approach compared to neglecting degrees of freedom.

Conclusions:

• The developed efficient TDMVCC implementation provides an accurate and computationally feasible method for studying nuclear quantum dynamics.
• Hybrid TDMVCC/TDH methods offer a promising route to further reduce computational cost while maintaining good accuracy.
• This work paves the way for applying advanced quantum dynamics simulations to larger and more complex molecular systems.