Related Experiment Video
Updated: Jun 27, 2026

Excitonic Hamiltonians for Calculating Optical Absorption Spectra and Optoelectronic Properties of Molecular Aggregates and Solids
Published on: May 27, 2020
Implementation of transition moments between excited states in the approximate coupled-cluster singles and doubles
1Institut für Physikalische Chemie, Universität Mainz, Jakob Welder-Weg 11, D-55099 Mainz, Germany. pabst@uni-mainz.de
Abstract:
An implementation of transition moments between excited states for the approximate coupled-cluster singles and doubles model (CC2) using the resolution of the identity (RI) approximation is reported. The accuracy of the RI approximation is analyzed for a testset of 7 molecules and 76 transitions. The RI error is found to be very small for both transition moments and oscillator strengths. Furthermore, the performance of the CC2 model in comparison with coupled-cluster singles and doubles (CCSD) is studied for 40 transitions of the same testset, yielding deviations of about 12% for the transition moments and 24% for the oscillator strengths. In addition, for 13 transitions of the testset the behavior of the transition moments with respect to seven different basis sets (Dunnings xaug-cc-pVXZ, with x=0,1,2 for X=D,T and x=2 for X=5) is analyzed, showing a strong dependence on the degree of augmentation x and a rather small effect of the cardinal number X. First applications are presented for the triplet-triplet transition moments of benzene and polyacenes (naphthalene to pentacene), showing good agreement with experimental and theoretical results for transitions between single excitation dominated states. Somewhat problematic is the insufficient description of double-excitation dominated states by the CC2 model. As transitions to such states may be strongly allowed, unlike for excitations out of the ground state, important features of transient spectra may be missed. For triplet-triplet excitations the problem is less evident as the lowest doubly excited triplet states are expected at higher energies.
Related Concept Videos
Transition State Theory
¹H NMR: Interpreting Distorted and Overlapping Signals
As Δν decreases and the signals move closer, the doublets appear increasingly distorted. The intensities of the inner lines increase at the cost of those of the outer lines as the signals are slanted or...
UV–Vis Spectroscopy: Molecular Electronic Transitions
Hybridization of Atomic Orbitals II
Double Resonance Techniques: Overview
Spin decoupling is usually achieved by...
Spin–Spin Coupling: Two-Bond Coupling (Geminal Coupling)
The central atom need not be NMR-active because its electrons are affected by the electron polarization of the spin-active atoms. However, spin information is transmitted less effectively than in one-bond coupling, and 2J values are usually weaker than 1J values. The energy of...
