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M. Hoffmann,
Mixing of Frenkel and Charge-Transfer Excitons and Their Quantum Confinement in Thin Films
in V. M. Agranovich and G. F. Bassani, Electronic Excitations in Organic Multilayers and Organic Based Heterostructures (Volume 31 of Thin Films and Nanostructures), pp. 221-292, Elsevier, Amsterdam, 2003

 
Contents
(page numbers refer to manuscript version for download)

1 Introduction 2
2 Electronic Frenkel and charge-transfer excitons in rigid one-dimensional crystals 7
2.1 Localized basis states in real and momentum space 7
2.2 Model Hamiltonians for Frenkel and charge-transfer states 9
2.3 Characters and transition dipoles of the eigenstates 16
2.4 Direction of charge-transfer transition dipoles 20
3 Strong coupling of the electronic excitations with internal phonon modes 25
3.1 Exciton-phonon coupling in the isolated molecule 25
3.2 The Holstein-Hamiltonian for exciton-phonon coupling 29
3.3 Basis functions for numerical diagonalization 30
3.4 Transition dipoles and phonon clouds of the eigenstates 34
3.5 Truncated phonon basis and symmetry adaptation 38
3.6 The limit for weak intermolecular electronic coupling 40
3.7 Numerical solutions for various electronic coupling strengths 44
3.8 The Holstein Hamiltonian with charge-transfer states 47
4 Applications and consequences for quantum confinement 53
4.1 Description of PTCDA-derivatives 53
4.2 Inclusion of finite size and quantum confinement effects 59
5 Conclusion 65
6 Acknowledgments 66
 

Illustrational Example: Fig. 14

This figure gives on overview of band structures in the Holstein model for fixed exciton phonon coupling constant g = 1 and various exciton hopping integrals J.
The four panels (a) - (d) show the transition from the molecular limit (J=0) to the adiabatic limit (illustrated by J = 2 hbar omega). The electronic bands E(k) are shown in the center of each panel. The spectra on the left side of each panel (for k = 0) correspond to absorption spectr
 
pdf file of manuscript version (897 KB)
 
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last updated: M. Hoffmann, 06 July 2006