Unitary coupled cluster ground- and excited-state molecular properties
A scheme for the calculation of molecular properties within the framework of unitary coupled-cluster (UCC) theory in both the electronic ground and excited states is presented. The scheme is based on an expectation-value ansatz, similar to the equation-of-motion coupled-cluster method or the interme...
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| Main Authors: | , |
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| Format: | Article (Journal) |
| Language: | English |
| Published: |
26 August 2020
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| In: |
The journal of chemical physics
Year: 2020, Volume: 153, Issue: 8 |
| ISSN: | 1089-7690 |
| DOI: | 10.1063/5.0019055 |
| Online Access: | Verlag, lizenzpflichtig, Volltext: https://doi.org/10.1063/5.0019055 Verlag, lizenzpflichtig, Volltext: https://aip.scitation.org/doi/full/10.1063/5.0019055 
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| Author Notes: | Manuel Hodecker, Andreas Dreuw |
| Summary: | A scheme for the calculation of molecular properties within the framework of unitary coupled-cluster (UCC) theory in both the electronic ground and excited states is presented. The scheme is based on an expectation-value ansatz, similar to the equation-of-motion coupled-cluster method or the intermediate state representation (ISR) approach of the algebraic-diagrammatic construction (ADC) scheme. Due to the UCC ansatz, the resulting equations cannot be given by closed-form expressions but need to be approximated. Explicit expressions for the expectation value of a general one-particle operator correct through second order in perturbation theory have been derived and coded for the electronic ground state as well as for excited states of predominant single-excitation character. The resulting equations are shown to be equivalent to those of the second-order ADC/ISR procedure. As first computational tests, the second-order UCC method (UCC2) and the one employing third-order amplitudes (also eigenvectors) together with the second-order density matrix, denoted as UCC3(2), are applied to the calculation of dipole moments for a series of small closed- and open-shell systems as well as 4-cyanoindole and 2,3-benzofuran and compared to full configuration interaction or experimental results. For the aromatic organic molecules, the UCC2 method is shown to be sufficient for the ground-state dipole moment, whereas the UCC3(2) scheme is superior for excited-state dipole moments. |
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| Item Description: | Gesehen am 12.10.2020 |
| Physical Description: | Online Resource |
| ISSN: | 1089-7690 |
| DOI: | 10.1063/5.0019055 |