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Bridging single and multireference coupled cluster theories with universal state selective formalism
Kiran Bhaskaran-Nair1, Karol Kowalski
1William R. Wiley Environmental Molecular Sciences Laboratory, Battelle, Pacific Northwest National Laboratory, K8-91, P.O. Box 999, Richland, Washington 99352, USA.
The Journal of Chemical Physics
|June 8, 2013
Summary
The universal state selective (USS) approach introduces new energy functionals to bridge single and multireference coupled cluster theories (SR/MRCC). This method ensures size-consistency, enhancing accuracy in quantum chemistry calculations.
Area of Science:
- Quantum Chemistry
- Theoretical Chemistry
- Computational Chemistry
Background:
- Coupled cluster theories are essential for accurate electronic structure calculations.
- Bridging single-reference (SR) and multireference (MR) coupled cluster (CC) theories remains a challenge.
- Existing methods may lack size-consistency, impacting accuracy for larger systems.
Purpose of the Study:
- To develop novel energy functionals using the universal state selective (USS) multireference approach.
- To enable a unified framework for both SR and MR coupled cluster theories.
- To ensure additive separability (size-consistency) of calculated energies.
Main Methods:
- Construction of new energy functionals based on the USS multireference formalism.
- Utilizing trial wavefunctions that guarantee size-consistency in the non-interacting subsystem limit.
- Combining the USS formalism with approximate SRCC theories to create a size-consistent MRCC method.
Main Results:
- The developed USS energy functionals offer a pathway to unify SR/MRCC theories.
- The approach ensures size-consistency, crucial for accurate calculations of molecular properties.
- The formalism can be viewed as a size-consistent version of the method of moments of coupled cluster equations.
Conclusions:
- The USS multireference approach provides a robust framework for developing accurate and size-consistent quantum chemical methods.
- This work facilitates the integration of single and multireference coupled cluster theories.
- The developed functionals hold promise for improved electronic structure calculations in various chemical applications.
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