The miniaturization of electronic circuits, which could ultimately be carried out by a single molecule placed between electrodes, as well as the improvement of experimental techniques for measuring current through a molecular junction, requires to develop increasingly accurate techniques for calculating the tunnelling current and its variations. In this thesis, we develop a multi-electronic calculation method of the transmission coefficient which is actually a generalization of the one-electron ESQC method. This procedure is based on the scattering matrix of the molecular junction written in a basis set of m+1 particles configurations: one incident particle, and m electrons localized, but not frozen, on the molecule. This method, named CI-ESQC, is then used to figure out the multi-particles mechanisms of charge transfer in the tunnel junction for resonant energies. Next, interferences between several resonances are studied, as well as the decay of the transmission coefficient with the length of a molecular wire in the junction. Finally the method is applied to a molecular junction likely to carry out frequency controlled logic gates.
