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Improving upon CCSD(T): LambdaCCSD(T). II. Stationary formulation and derivatives
Andrew G Taube1, Rodney J Bartlett
1Quantum Theory Project, University of Florida, Gainesville, Florida 32608, USA.
The Journal of Chemical Physics
|February 6, 2008
Summary
The new Lambda coupled-cluster (CC) method significantly improves calculations of bond breaking. While similar for transition states, Lambda CC theory shows overall superiority for force curves compared to CCSD(T).
Area of Science:
- Quantum Chemistry
- Computational Chemistry
Background:
- Coupled-cluster (CC) theory is a cornerstone of quantum chemistry for accurate electronic structure calculations.
- Standard methods like CCSD(T) struggle with describing bond breaking accurately, particularly away from equilibrium geometries.
Purpose of the Study:
- To introduce and implement analytical derivatives for the LambdaCCSD(T) method.
- To evaluate the performance of LambdaCCSD(T) in describing bond breaking and chemical reactions.
Main Methods:
- Formulation and implementation of analytical derivatives for the LambdaCCSD(T) method.
- Application of the method to diatomic force curves and transition states of chemical reactions.
Main Results:
- LambdaCCSD(T) provides a vastly superior treatment of bond breaking compared to CCSD(T).
- For transition states, LambdaCCSD(T) and CCSD(T) yield very similar structures and activation barriers.
- Diatomic force curves clearly demonstrate the overall superiority of LambdaCCSD(T).
Conclusions:
- LambdaCCSD(T) represents a significant advancement in single-reference CC theory, enhancing accuracy for systems with significant bond dissociation.
- The method paves the way for further generalizations of CC theory to improve accuracy in describing challenging chemical phenomena.
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