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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
Published on: April 8, 2020
Partially linearized, fully size-extensive, and reduced multireference coupled-cluster methods. I. Formalism and
1Department of Applied Mathematics, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada. xli@scienide.uwaterloo.ca
The Journal of Chemical Physics
|April 17, 2008
Summary
A new computational chemistry method, partially linearized (pl) MR CCSD, offers a size-extensive alternative for calculating electronic structures. It efficiently approximates higher-order cluster amplitudes for improved accuracy in quantum chemistry calculations.
Area of Science:
- Quantum Chemistry
- Computational Chemistry
- Theoretical Chemistry
Background:
- Coupled-cluster (CC) methods are essential for accurate electronic structure calculations.
- Reduced multireference (RMR) coupled-cluster methods offer a balance between accuracy and computational cost.
- Size-extensivity is a crucial property for accurate calculations of extended systems.
Purpose of the Study:
- To introduce a fully size-extensive alternative to the RMR coupled-cluster method.
- To develop a computationally tractable approach for including higher-than-pair cluster amplitudes.
- To present the partially linearized (pl) MR CCSD method and its extension, plMR CCSD(T).
Main Methods:
- Linearization of full CC equations projected onto higher-than-doubly excited configurations.
- Selection of a subset of primary higher-than-pair cluster amplitudes based on RMR CCSD criteria.
- Inclusion of secondary triples via standard (T)-type corrections for the plMR CCSD(T) variant.
Main Results:
- The proposed partially linearized (pl) MR CCSD method provides a size-extensive alternative.
- This approach incorporates higher-than-triples (up to hexuples) amplitudes efficiently.
- The plMR CCSD(T) extension is also presented, incorporating secondary triples.
Conclusions:
- The plMR CCSD method offers a promising avenue for accurate and efficient electronic structure calculations.
- The study establishes the relationship between RMR and plMR CCSD/CCSD(T) approaches.
- Further investigation into the performance and characteristics of these methods is detailed in Part II.
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