Testing the condon approximation for electron transfer via the Mulliken-Hush model

For nonadiabatic electron-transfer reactions, it is common to make a Condon approximation assumption that the mixing matrix element is independent of nuclear geometry. We test the validity of the Condon approximation using Mulliken-Hush analysis applied to the biphenyl alcohol molecule at various geometries. Calculations of the energy splitting and electronic coupling matrix element as functions of geometry using semiempirical and ab initio methods are presented. Breakdown of the Condon approximation is observed, quantified, and analyzed.