Classical anharmonic chain

The chemical structure dependence of electronic hyperpolarizability is discussed. Strategies for developing structure-function relationships for nonlinear optical chromo-phores are presented. Some of the important parameters in these relationships, including the relative ionization potential of reduced donor and acceptor and the chain length, are discussed. The correspondence between molecular orbital and classical anharmonic oscillator models for nonlinear polarizability is described. 

In the genera anisotropic case, P has to be replaced by the components of the stress tensor and V by the components of the deformation tensor (Sect.3.6)]. We shall formulate the problem quantum mechanically but we often orientate ourselves by the results obtained for the classical linear chain. In particular, we use the quasi harmonic approximation, that is, we neglect the specific anharmonic term [see (5.42) for the linear chain]. Thus... 

As an introduction, the chapter begins with the anharmonic diatomic molecule. Then we study the thermal properties (free energy, equation of state, thermal expansion and specific heat) of the classical anharnx)nic linear chain. Two important concepts are introduced the Gvuneisen pavametev and the quasiharmonic approximation. In this approximation, the temperature dependence of the force constants and phonon frequencies is only due to the... 

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