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Nitrogen Compound Characterization in Fuels by Multidimensional Gas Chromatography
Published on: May 15, 2020
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Assessing the distinguishable cluster approximation based on the triple bond-breaking in the nitrogen molecule
Varun Rishi1, Ajith Perera1, Rodney J Bartlett1
1Quantum Theory Project, University Of Florida, Gainesville, Florida 32611, USA.
The Journal of Chemical Physics
|April 3, 2016
Summary
New Distinguishable Cluster (DC) methods improve ab initio calculations for breaking multiple bonds, like in nitrogen (N2). These advanced coupled cluster (CC) approaches offer better potential energy curves than traditional methods.
Area of Science:
- Quantum Chemistry
- Computational Chemistry
- Theoretical Chemistry
Background:
- Accurate potential energy curves for multiple bond dissociation are challenging for ab initio methods, especially coupled cluster (CC) methods like CCSD and CCSD(T).
- The choice of spin-restricted reference functions can negatively impact the accuracy of these calculations.
- Existing CC methods struggle with complex bond dissociation processes, particularly when multiple bonds break simultaneously.
Purpose of the Study:
- To investigate and generalize the Distinguishable Cluster (DC) approach for improved ab initio calculations of bond dissociation.
- To assess the performance of DC and other approximate CC methods for the challenging nitrogen molecule (N2) bond-breaking problem.
- To evaluate the utility of spatial symmetry-broken Hartree-Fock (HF) solutions as references for correlated calculations.
Main Methods:
- Detailed study of approximate coupled cluster methods, including the Distinguishable Cluster (DC) approach.
- Application of DC, ACCD, ACP-D45, ACP-D14, 2CC, and pCCSD(α, β) to nitrogen molecule bond dissociation.
- Generalization of the DC method to unrestricted HF (UHF) references (DCD, DCSD), inclusion of triples corrections (DCSD(T), DCSDT-n), and application of the equation of motion (EOM) approach (EOM-DCD, EOM-DCSD).
Main Results:
- DC methods show promise in overcoming deficiencies in bond dissociation calculations, particularly for quasi-degenerate situations.
- UHF-based CC and DC methods exhibit similar performance for N2 bond-breaking.
- Using spatially broken but spin-preserving SCF references improves CCSD solutions compared to DCSD.
Conclusions:
- The Distinguishable Cluster approach offers a viable strategy to improve the accuracy of ab initio potential energy curves for multiple bond dissociation.
- Generalized DC methods, including those based on UHF and EOM-CC, provide valuable tools for studying complex chemical processes.
- Spatial symmetry breaking in reference functions can enhance the performance of correlated calculations where standard methods fail.
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