The Dose Makes the Poison: Perturbative Steps toward the Ultimate Linearized Coupled Cluster Method.

Area of Science:

• Quantum Chemistry
• Computational Chemistry
• Theoretical Chemistry

Background:

• Coupled cluster (CC) methods are vital for accurate electronic structure calculations.
• Strong correlation poses a significant challenge for standard CC approaches.
• Linearized CC methods offer computational advantages but struggle with divergences.

Purpose of the Study:

• To address the underestimation of dynamical correlation in linearized ladder CCD (linLCCD).
• To develop a robust and accurate CC method for strongly correlated systems.
• To improve upon existing linearized CC techniques.

Main Methods:

• Introduction of a linearized external coupled cluster perturbation theory.
• Incorporation of a second-order ring/crossed-ring correction.
• Development of the xlinCCD(2) method based on linLCCD.

Main Results:

• The xlinCCD(2) method avoids singularities encountered in other linearized CC approaches.
• xlinCCD(2) successfully incorporates dynamical correlation effects.
• The new method achieves results comparable to linearized CCD in weakly correlated systems.

Conclusions:

• The developed xlinCCD(2) method offers a promising solution for treating strong correlation.
• This approach enhances the accuracy of linearized CC methods.
• xlinCCD(2) provides a computationally feasible and accurate alternative for electronic structure studies.