Nuclear relaxation hyperpolarizabilities

Apart from purely electronic effects, an asymmetric nuclear relaxation in the electric field can also contribute to the first hyperpolarizability in processes that are partly induced by a static field, such as the Pockels effect [55, 56], and much attention is currently devoted to the study of the vibrational hyperpolarizability, can be deduced from experimental data in two different ways [57, 58], and a review of the theoretical calculations of p, is given in Refs. [59] and [60]. The numerical value of the static P is often similar to that of static electronic hyperpolarizabilities, and this was rationalized with a two-state valence-bond charge transfer model. Recent ab-initio computational tests have shown, however, that this model is not always adequate and that a direct correlation between static electronic and vibrational hyperpolarizabilities does not exist [61]. 

Table 14 Electronic and nuclear relaxation contributions to the polarizabilities and hyperpolarizabilities of structures I, ref 96. Static and infinite frequency limit values are given for pnr(—co a>, 0)...

Keywords nonlinear optical properties, vibrational hyperpolarizabilities, nuclear relaxation hyper-... 

Based on the nuclear relaxation/curvature approach it is natural to divide the total hyperpolarizability into two different perturbation sequences [37] ... 

Costa et al. present results of many-body perturbation theory, coupled cluster and quadratic Cl methods apphed to the calculation of the polarizability and first hyperpolarizability of NaH. It is shown that the nuclear relaxation contribution is substantial for this molecule and that it is appreciably affected by electron correlation effects. 

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