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Unitary coupled cluster ground- and excited-state molecular properties.
- Source :
-
Journal of Chemical Physics . 8/28/2020, Vol. 153 Issue 8, p1-10. 10p. 4 Charts. - Publication Year :
- 2020
-
Abstract
- 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. [ABSTRACT FROM AUTHOR]
- Subjects :
- *DIPOLE moments
*EXCITED states
*PERTURBATION theory
*DENSITY matrices
*EIGENVECTORS
Subjects
Details
- Language :
- English
- ISSN :
- 00219606
- Volume :
- 153
- Issue :
- 8
- Database :
- Academic Search Index
- Journal :
- Journal of Chemical Physics
- Publication Type :
- Academic Journal
- Accession number :
- 145434411
- Full Text :
- https://doi.org/10.1063/5.0019055