Coulomb coupling

In addition to the entropy term we assume that there is an extra local coupling between the fields via and, in addition to the coulombic coupling which is long range, we assume the existence of a short-range non-local coupling via We can choose several functional forms to... 

Madjet, M. E., E. Abdurahman, and T. Renger. 2006. Intermolecular Coulomb couplings from ab initio electrostatic potentials Application to optical transitions of strongly coupled pigments in photo synthetic antennae and reaction centers. J. Phys. Chem. B 110 17268-17281. 

The magnitude of the off-diagonal Hamiltonian (i.e. the energy transfer rate) thus depends on the strengths of the electron-phonon and Coulombic couplings and also the overlap of the two exciton wavefunctions[53]. Energy transfer rates from states to state jx, are calculated via the golden rule [54] and used as inputs to a master equation calculation of the excitation transfer kinetics in PSI, in which the dynamical information is included in the matrix K. 

The TDC method takes into account the shape of the molecules in detail, and its accuracy in the calculation of the Coulomb coupling depends only on the size of the volume elements used in the grid (the cube ). In this way, the TDC method has proven extremely useful in understanding the limitations of the point dipole approximation (PDA) in a variety of systems. In particular, how the PDA fails to describe the coupling when the interchromophoric center-to-center distance is comparable to the molecular dimensions, a situation found, for example, in many of the relevant interactions present in natural light-harvesting antennas. [50]... 

A further recent advance in the field has been the development of ab initio QM approaches able to compute analytically the Coulomb coupling between... 

Fig. 5 Coulomb coupling between Pheo m and n formulated in terms of atomic centered partial charges (transition charges) qml,. and qnv, Eq. (18).

Fig. 3 Coulombic coupling between the lowest tttt transition moments of Watson Crick AT base pair (left) and two stacked and parallel Ts (right) as a function of the distance between the two bases. The distance is measured between N1 and N3 atoms of A and T, respectively, for the AT pair (left) and between the centers of the mases of the two Ts (right). (From Ref. [23])...

The simplest Frenkel exciton model consists of diagonal energies en representing the exciton energies of the individual bases with off-diagonal elements corresponding to the Coulomb coupling between exciton states, J... 

When D and A are substantially separated in space, FCoul reduces to the dipole approximation discussed above. If the center-to-center distance R is comparable with the size of the molecules involved, then the dipole approximation may not provide an accurate representation of VCoul. This is because information regarding the shape of the interacting molecules is discarded when the dipole approximation, or even a low-order multipole expansion, is invoked [7,11,12], In particular, molecules with extended or asymmetric transition densities tend to exaggerate errors in the dipole-dipole approximation. In this case, information on transitions of each molecule should be retained as a transition density, rather than a dipole transition moment [36,37]. The Coulombic coupling... 

Figure 3.17 Time evolution of the ISe ISh exciton population as a function of the relaxation times and Coulomb coupling for the single and biexcitons. The rise time of the biexciton (formation time) and the presence of strong or damped quantum beating depends upon the relative values of the Wc, yi, and j2 as shown above. Source Shabaev et al. (2006).

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