This work studies the modelling of the incommensurate inclusion compounds n-alkane/urea using the double-chain model (DCM) to investigate the existence of a phason or sliding mode. The 1D DCM is applied to heptadecane/urea and shows a small window for a gapless phason mode. Then the model is generalized to 2D. From a variety of possible models an iterative model was chosen for numerical reasons. The structure was found to converge in 6 steps, irrespective of the use of random shifts of the alkane chains. So, there is indirect interaction between neighbouring alkane chains via the urea chain.