Polarisation and Band Structure

Typical values for the magnitude of the Davydov splitting for triplet states he in the region of 10 cm and for singlet states between 100 and some 1000 cm, as we have already mentioned for dimers. 

In Table 6.1, some numerical values for the Si and Ti states in anthracene and naphthalene are collected. 

When vibrons and phonons are thermally populated, then all possible k values are occupied. With the selection rule Afe = 0, it is clear that absorption transitions 

For the quantities given in this table, slightly differing values can be found in the literature. We dispense here with a detailed discussion and literature citations. 

To compute the complete exciton dispersion relations E(k), we start from Eqns. (6.16)-(6.18). Denoting the two possible sites within the unit cell by A and B, we write the fe-dependent part of the energy as  

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