Ab initio investigation of doping-enhanced electronic and vibrational second hyperpolarizability of polyacetylene chains

The effect of charging on the longitudinal second hyperpolarizability of polyacetylene chains containing upto 70 carbon atoms were examined using ab initio calculations. Isolated solitonic chains as well as chains with an explicit alkali atom were considered as dopants. As the size of the alkali atom increased, the hyperpolarizabilities approached those of the isolated chains. The geometry, degree of charge transfer, and relative site stability were determined at RHF/6-31G level, while the static electronic and vibrational contributions to the hyperpolarizability were obtained using the CPHF/6-31G computational scheme.