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Coupled-cluster theory with simplified linear-r(12) corrections: the CCSD(R12) model
Heike Fliegl1, Wim Klopper, Christof Hättig
1Lehrstuhl für Theoretische Chemie, Institut für Physikalische Chemie, Universität Karlsruhe (TH), D-76128 Karlsruhe, Germany. heike.fliegl@chem.bio.uni-karlsruhe.de
The Journal of Chemical Physics
|April 20, 2005
Summary
A new coupled-cluster model, CCSD(R12), approximates linear-r(12) corrections effectively. This computational chemistry method offers accurate energy contributions for atoms and molecules, outperforming simpler models.
Area of Science:
- Computational Chemistry
- Quantum Chemistry
- Theoretical Chemistry
Background:
- Coupled-cluster theory is a powerful method for electronic structure calculations.
- Linear-r(12) methods incorporate inter-electron distances to accelerate basis set convergence.
- Accurate calculations are crucial for understanding molecular properties.
Purpose of the Study:
- To propose and validate a simplified coupled-cluster model with linear-r(12) corrections, denoted CCSD(R12).
- To compare the performance of CCSD(R12) against the established CCSD-R12 method.
- To assess the basis-set convergence of the new model.
Main Methods:
- Development of the CCSD(R12) model, a simplified singles-and-doubles coupled-cluster approach.
- Utilizing an orthonormal auxiliary basis set and resolution-of-the-identity approximation for integral calculations.
- Investigating basis-set convergence for atoms and small molecules.
Main Results:
- The CCSD(R12) model provides an excellent approximation to the full linear-r(12) energy contribution in large basis sets.
- The simplified model demonstrates good agreement with the more computationally intensive CCSD-R12 method.
- Second-order perturbation theory significantly overestimates the linear-r(12) contribution.
Conclusions:
- CCSD(R12) offers an efficient and accurate way to include important correlation effects.
- The proposed model is a viable alternative for electronic structure calculations where computational cost is a concern.
- Accurate treatment of electron correlation is essential for reliable theoretical predictions.