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Computation of Atmospheric Concentrations of Molecular Clusters from ab initio Thermochemistry
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Third-Order Unitary Coupled Cluster (UCC3) for Excited Electronic States: Efficient Implementation and Benchmarking
Manuel Hodecker1, Sebastian M Thielen1, Junzi Liu2
1Interdisciplinary Center for Scientific Computing, Heidelberg University, Im Neuenheimer Feld 205, D-69120 Heidelberg, Germany.
Journal of Chemical Theory and Computation
|May 13, 2020
Summary
The study presents an efficient implementation of the third-order unitary coupled-cluster (UCC3) scheme for calculating excited electronic states. UCC3 and UCC2 methods accurately predict excitation energies and oscillator strengths for organic molecules.
Area of Science:
- Computational Chemistry
- Quantum Chemistry
- Theoretical Chemistry
Background:
- Accurate calculation of excited electronic states is crucial for understanding molecular properties and reactivity.
- Existing methods for calculating excitation energies and oscillator strengths have limitations in accuracy and efficiency.
Purpose of the Study:
- To report the efficient implementation of the third-order unitary coupled-cluster (UCC3) scheme.
- To benchmark and compare the performance of UCC3 and its second-order variant (UCC2) against established datasets for excitation energies and oscillator strengths.
Main Methods:
- Implementation of the third-order unitary coupled-cluster (UCC3) scheme.
- Calculation of 134 excited singlet and 71 excited triplet states for 28 organic molecules.
- Comparison with benchmark sets from Jacquemin and Thiel.
Main Results:
- UCC2 showed mean errors of 0.36 ± 0.41 eV (singlet) and 0.22 ± 0.21 eV (triplet).
- UCC3 demonstrated higher accuracy with mean errors of 0.06 ± 0.27 eV (singlet) and -0.22 ± 0.15 eV (triplet).
- Oscillator strengths calculated with effective transition moments agreed well with literature data.
Conclusions:
- The UCC3 scheme provides a highly accurate and efficient method for calculating excited electronic states.
- Both UCC2 and UCC3 are valuable tools for theoretical studies of molecular excitation properties.
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