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Updated: May 18, 2026
Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
Published on: April 8, 2020
Communication: Restoring full size extensivity in internally contracted multireference coupled cluster theory
Matthias Hanauer1, Andreas Köhn
1Institut für Physikalische Chemie, Universität Mainz, D-55099 Mainz, Germany. hanauem@uni-mainz.de
This study resolves size extensivity issues in internally contracted multireference coupled cluster theories by modifying how redundant cluster operator components are removed. The new method ensures accurate calculations for larger chemical systems.
Area of Science:
- Quantum Chemistry
- Computational Chemistry
Background:
- Internally contracted multireference coupled cluster (icMRCC) theories are powerful quantum chemistry methods.
- Current implementations suffer from a lack of size extensivity in the valence space.
Purpose of the Study:
- To address and resolve the size extensivity problem in valence space for icMRCC theories.
- To present a straightforward method for restoring size extensivity.
Main Methods:
- The core issue lies in the procedure for eliminating redundant components of the cluster operator.
- The proposed solution involves performing this elimination in a specific basis of excitation operators.
- These operators are normal ordered with respect to the multiconfigurational reference function.
Main Results:
- Full size extensivity is restored in the valence space.
- The modified procedure is simple and effective.
Conclusions:
- The presented method offers a significant improvement for multireference coupled cluster calculations.
- Accurate and scalable electronic structure calculations are now more achievable.
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