Transport diffusion of argon in the unidirectional channels of the molecular sieve AlPO4-5 has been studied using molecular dynamics simulations. Using the Green-Kubo formalism, this nonequilibrium property is, for the first time, extracted from just one equilibrium simulation. Apart from the computational advantages above nonequilibrium simulations, the new method also provides a way to check the validity of the assumption of linear response, which is at the basis of both methods. The transport diffusion coefficient for argon at 87 K and half the maximum loading is found to be equal to D-t=(1.4 +/-0.1)x10(-5) cm(2)/s, of which approximately 20% can be attributed to correlated, collective motion.