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Exciton Theory with Correlation

It is well known that in the HF theory of a closed-shell atom or of a finite molecule, the singlet excitation energy from a filled level i to an unfilled level a is given by the expression [Pg.271]

In this way we are left with too large an excitation energy, because equation (8.1) for an infinite system reduces to the HF gap (which is too large anyway). [Pg.271]

However, in insulator solids or long linear chains possessing a band structure with delocalized electrons, a new physical phenomenon must be taken into account, namely, interaction between the excited electron and the remaining, positive hole in the valence band. This interaction in molecular crystals in usually described with the help of the simplest form of exciton theory, so-called Frenkel exciton theory (see, e.g., Knox ) which assumes that the excited electron and the remaining positive hole can be found in the same unit cell. [Pg.271]

The intermediate exciton theory of Takeuti [which applied some empirical parameters and assumed parabolic curves e(fc) effective mass approximation] was developed in an ab initio form without any empirical parameters, using not HF but quasi-particle (QP) one-electron energies (see Section 5.3) by Suhai.  [Pg.272]

The mathematical formulation of the theory of interaction between an electron and a hole starts from the Hamiltonian operator H (in second quantization and atomic units) given by [Pg.272]


In a subsequent calculation the intermediate exciton theory with correlation was applied to a cytosine stack, the superimposed cytosine molecules possessing the same relative geometry as in the in vivo stable DNA B. In this calculation, only a double-C basis was applied (no polarization functions) owing to the rather large size of the unit cell (a cytosine molecule). ... [Pg.281]

The next step was the discussion of electronic correlation both in larger molecules and in polymers. In his lectures Collins developed a general theory using the Green s function formalism for the excitons in polymers and solids as well as for the possibility of excitonic superconductivity in CuCl and CdS. The lectures of Kunz have covered both the problems of ground state correlation and the calculation of excitons including correlation. In the one hour lecture of Suhai the question of the excitonic spectra with correlation was also discussed and he has presented results for polyethylene. [Pg.431]

Rapid convergence at large alternation is expected on general grounds. The sufficiency of N = 14 oligomers for linear or TPA spectra of Hubbard and PPP chains with 5 > 0.6 follows in detail from molecular exciton theory [116]. The different shapes of PPP and Hubbard crossovers in Fig. 6.15 are due to different B states, which are in turn related to Vpp- in Eq. (7) B is an exciton in PPP theory [134] and evolves [116] to an excited dimer at 5 = 1, while B is a CT state [37] in Hubbard chains at 5 1. These possibilities for B are another generic feature of Eq. (7). Molecular PPP parameters place [133] PA on the correlated side, PS and PPV on the band side. [Pg.188]

No correlation calculations have been performed until now on biopolymers, but such computations have been successfully executed in the cases of polymers with small unit cells (transpolyacetylene and polydiacetylene see below). The same holds for exciton spectra which have been successfully computed applying intermediate (charge transfer) exciton theory /5/ for the above mentioned two chains /6/. One should mention, however, that only the inclusion of the major part of correlation resulted in results in reasonable agreement with experiment. There is an early calculation on transport properties of periodic DNA models using simple tight binding (Huckel) band structures /7/. In the... [Pg.338]

Our interest in quantum dot-sensitized solar cells (QDSSC) is motivated by recent experiments in the Parkinson group (UW), where a two-electron transfer from excitonic states of a QD to a semiconductor was observed [32]. The main goal of this section is to understand a fundamental mechanism of electron transfer in solar cells. An electron transfer scheme in a QDSSC is illustrated in Figure 5.22. As discussed in introduction, quantum correlations play a crucial role in electron transfer. Thus, we briefly describe the theory [99] in which different correlation mechanisms such as e-ph and e-e interactions in a QD and e-ph interactions in a SM are considered. A time-dependent electric field of an arbitrary shape interacting with QD electrons is described in a dipole approximation. The interaction between a SM and a QD is presented in terms of the tunneling Hamiltonian, that is, in... [Pg.299]

In order to correlate the solid state and solution phase structures, molecular modelling using the exciton matrix method was used to predict the CD spectrum of 1 from its crystal structure and was compared to the CD spectrum obtained in CHC13 solutions [23]. The matrix parameters for NDI were created using the Franck-Condon data derived from complete-active space self-consistent fields (CASSCF) calculations, combined with multi-configurational second-order perturbation theory (CASPT2). [Pg.233]

The annihilation rate constant in PS II is much the same as in PS I, as found by analogous measurements but with an irreversible reaction scheme. This correlates with the similar structure and pigment composition of the two antenna systems of higher plants and shows that this functional parameter is rather independent of the mechanism (irreversible/ reversible) and the rate of trapping. If in analogy to the theory of exciton dynamics for... [Pg.1265]

Computational methods such as molecular mechanics (MM) and quantum theory calculations have become convenient and reliable techniques in the analysis of CD data. A common approach in chiral supramolecular structural study is to examine if a supramolecular conformation simulated by MM method is consistent with the observed CD spectrum of the sample. However, in order to use this approach, one needs to correlate the stereostructures and CD data by using, for example, exciton chirality method or reference CD spectra of analogs with known structures. Thus, it should be noted that the application of this method has some limitations for evaluation in supramolecular systems. [Pg.463]


See other pages where Exciton Theory with Correlation is mentioned: [Pg.271]    [Pg.273]    [Pg.275]    [Pg.277]    [Pg.271]    [Pg.273]    [Pg.275]    [Pg.277]    [Pg.127]    [Pg.58]    [Pg.187]    [Pg.106]    [Pg.6]    [Pg.187]    [Pg.187]    [Pg.592]    [Pg.601]    [Pg.601]    [Pg.62]    [Pg.3]    [Pg.4]    [Pg.269]    [Pg.24]    [Pg.340]    [Pg.117]    [Pg.143]    [Pg.15]    [Pg.17]    [Pg.25]    [Pg.114]    [Pg.811]    [Pg.98]    [Pg.67]    [Pg.95]    [Pg.200]    [Pg.202]    [Pg.103]    [Pg.301]    [Pg.3]    [Pg.548]    [Pg.948]    [Pg.107]    [Pg.205]    [Pg.177]    [Pg.112]   


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