Owing to remarkable advances on chemical synthesis combined with scanning probe microscopy and break junction techniques, conduction through molecular systems such as individual molecules or wires has been the focus of many experimental efforts on nanostructures in recent years.
The current understanding of such measurements points to the distinction between intrinsic factors e.g. `electron-phonon' coupling and extrinsic factors related to the contact at the molecular junction which determine the conductance. In the present work, we employ the Landauer theory which relates the conductance to a scattering problem to study in detail the contact effects on electron transport across a molecular wire sandwiched between two semi-infinite carbon nanotube leads with open ends. This allowes us to obtain the conductance as a function of system parameters such as the coupling strength, the dimensionality and geometry of contacts and electrodes. Implications for experiments are also discussed.