Extended vibrational coupled cluster: Stationary states and dynamics

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Vibrational coupled cluster (VCC) theory is a powerful tool for studying molecular vibrations.
• Existing VCC methods have limitations in accurately describing complex vibrational dynamics.
• The development of advanced theoretical frameworks is crucial for precise quantum mechanical calculations.

Purpose of the Study:

• To derive and implement equations for extended vibrational coupled cluster (EVCC) for stationary states.
• To develop time-dependent EVCC (TDEVCC) for propagating nuclear wave packets.
• To analyze the performance and convergence properties of EVCC and TDEVCC compared to traditional methods.

Main Methods:

• Derivation of equations for EVCC and TDEVCC, including energies, properties, and auto-correlation functions.
• Development of a new full-space framework for implementing alternative VCC variants.
• Testing of EVCC[k] and TDEVCC[k] on 35 three- and six-mode molecular systems.

Main Results:

• EVCC and TDEVCC demonstrated good, hierarchical convergence towards the exact limit for molecular systems.
• The new methods showed better convergence than normal VCC and TDVCC, and vibrational configuration interaction.
• Analysis highlighted the importance of exponential parameterizations and separability, particularly for TDEVCC bra parameterization.

Conclusions:

• EVCC and TDEVCC provide accurate and efficient methods for calculating vibrational states and dynamics.
• The developed framework facilitates the implementation of advanced coupled cluster variants.
• The findings are relevant to broader applications of coupled cluster theory in quantum chemistry.