BOND-ORBITAL THEORY OF LINEAR AND NONLINEAR ELECTRONIC RESPONSE IN IONIC-CRYSTALS .2. NONLINEAR RESPONSE

A bond-orbital theory of linear electronic response set out in the preceding companion paper (I) is expanded to include nonlinear response. Attention is focused on the third-order susceptibility ijkl(3) (particularly as measured by the nonlinear refractive index n2) in pretransition-metal halides and chalcogenides. Root-mean-square accuracy over 11 halides for relative n2 values is about 9%, and points to an essential absence of local-field effects in bond-orbital response at least for halides. The latter conclusion enables us to make an absolute calibration for n2a question of some considerable controversy among different experimental groups. © 1990 The American Physical Society.