  The results of spin-polarized density functional theory calculations find
that band gap engineering can be achieved by site-specific interactions in a
composite consisting of polyaniline and TiO2 nanoparticles. Interactions in the
composite matrix are found to be mediated by Ti atoms inducing dependency of
location of the conduction band minimum on the polyaniline site which is being
probed by TiO2. This dependency is due to subtle changes in the nature of
valance or conduction states near Fermi level introduced by the interacting
matrix sites. The results therefore suggest that optimization of the synthesis
parameters at atomic level can be an effective way to improve performance of a
photovoltaic device based on PAni- TiO2 composite.
