Comparison of the centrosymmetric and noncentrosymmetric models.
For the noncentro symmetric anharmonic oscillator described by Eq. (1.4.1), derive an expression for the third-order displacement x˜(3) and consequently for the third-order susceptibility χ(3) 1111(ωq ,ωm,ωn,ωp). Compare this result to that given by Eq. (1.4.52) for a purely centro symmetric medium. Note that for a noncentrosymmetric medium both of these contributions can be present. Estimate the size of each of these contributions to see which is larger.
