where σ represents the spin up/down electrons. The coupling of the central region to the electrodes is taken into account using self-energies, which are calculated by using a rather simpler wide-band limit approximation, which assumes that the density of states (DOS) of the electrode is independent of energy. A constant value of 0.036 taken from the literature is used for the DOS of the electrode. The zero bias conductance for a open shell radical system is then obtained as: