Unitary coupled cluster ground- and excited-state molecular properties

• Verfasst von: Hodecker, Manuel [VerfasserIn]
• Verfasst von: Dreuw, Andreas [VerfasserIn]
• Titel: Unitary coupled cluster ground- and excited-state molecular properties
• Verf.angabe: Manuel Hodecker, Andreas Dreuw
• E-Jahr: 2020
• Jahr: 26 August 2020
• Umfang: 10 S.
• Fussnoten: Gesehen am 12.10.2020
• Titel Quelle: Enthalten in: The journal of chemical physics
• Ort Quelle: Melville, NY : American Institute of Physics, 1933
• Jahr Quelle: 2020
• Band/Heft Quelle: 153(2020,8) Artikel-Nummer 084112, 10 Seiten
• ISSN Quelle: 1089-7690
• DOI: doi:10.1063/5.0019055
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 1735410195

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.