The intermediate-coupling regime

The 2 A+ state, with an energy lower than the l H state, is predominately a bimagnon. The particle-hole separations in the holon-doublon channel, Vp, defined by eqns (6.26) and (6.34) are also shown. 

consider 6 = 0.2. Fig. 6.10(b) shows that the four lowest essential states appear to fit the weak-couphng model, as they are the l B, and 4 B  

Since the state has large dipole moments to both the 2 A+ and 6 A+ 

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In the intermediate-coupling regime Mott-Wannier excitons are the more appropriate description for large dimerization (J = 0.2), while for the undimerized chain Mott-Hubbard excitons are the correct description. For dimerizations relevant to polyacetylene and polydiacetylene (that is, S ... 

This places polyacetylene and polydiacetylene on the correlated side of the intermediate-coupling regime. 

This argument breaks down when charge fluctuations are suppressed in favour of spin-density wave fluctuations. As described in Chapter 5 this occurs in the intermediate-coupling regime, around U At. 

The applicability of the reaction-rate formula in the intermediate-friction regime to the interpretation of conformational changes of bi-naphtyl in solution has been discussed.47 The intramolecular motion is governed by a bistable potential depending on a single variable, which is identified with the dihedral angle between the naphthalene moieties in binaphtyl. The influence of hydrodynamic interactions and coupling with the other coordinates of the molecules also are evoked. 

For C60, the coupling is in fact presumably in an intermediate coupling regime, so that all these effects should be taken into account and JT distortions could manifest themselves in a variety of ways. However, the previous classical treatment is very useful as a starting basis to get an intuitive idea of the situation and will be introduced now. The principle of the calculation is not fundamentally different than in the previous simple model, although symmetry considerations become more complicated as the number of modes involved increases, as well as their degeneracy. 

As in the model of Section IV.A.e, eigenstates with small imaginary parts (Va < 7c) exist. These states lead to a much slower regime of incoherent emission, with the rate corresponding to a single domain (yA — ny0). Numerical calculations are probably the best way to study the regime of emission in the intermediate-coupling case (T0 A ).141... 

A number of theories have been proposed to evaluate the ET rate in this intermediate coupling regime. For the present model (eqn (12.21)), Zusman formula predicts the rate expression as follows ... 

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