Computation of expectation values from vibrational coupled-cluster at the two-mode coupling level

Area of Science:

• Quantum chemistry
• Computational spectroscopy
• Molecular dynamics

Background:

• Calculating zero-point vibrational energy (ZPVE) averages is crucial for accurate molecular property prediction.
• Existing methods for ZPVE calculations can be computationally intensive, limiting their application to larger systems.
• The vibrational coupled-cluster (VCC) method offers a powerful framework for these calculations.

Purpose of the Study:

• To present a computationally efficient vibrational coupled-cluster method for calculating zero-point vibrational averages of properties.
• To demonstrate the scalability and applicability of the method to various molecular systems.
• To introduce a novel algorithmic approach for computing expectation values.

Main Methods:

• Utilizing the vibrational coupled-cluster method at the two-mode coupling level.
• Developing a technique to compute any expectation value using a single iterative solution of linear equations.
• Employing Lagrangian multipliers for efficient computation.

Main Results:

• The proposed algorithm exhibits a computational scaling of only the third power of the number of modes.
• This favorable scaling significantly enhances accessibility for calculations on larger molecular systems.
• Successful applications were demonstrated for water, pyrrole, and para-nitroaniline.

Conclusions:

• The presented vibrational coupled-cluster method provides an efficient and scalable approach for calculating zero-point vibrational averages.
• The developed technique offers a practical solution for studying larger and more complex molecular systems.
• This work advances the capabilities of computational chemistry for property prediction.