  We present a study of the charge transmission behavior of a series of dithiol
polyenes in the context of molecular junctions. Using the Landauer theory and
zero voltage approximation the Green's functions of the inserted molecules are
calculated from a fully ab initio wave function based procedure. Various
possibilities in approximating the correlation space are explored and
quantitatively evaluated. Our results show that the transmission behavior of a
molecular junction is not a monotonic function of the length of the employed
molecule. Moreover we introduce the analytic solution of a suitable model
system to countercheck the ab initio results and find a remarkable degree of
correspondence.
