The linear particle density along the outer ring is estimated by considering the armchair structure of the (40, 40) nanotube. Around the complete circumference, 160 atoms are associated with each ring as depicted in Fig. . Therefore, we let A = 160/(2πR o ). The final result is plotted and shown in Fig. . Also, shown in the figure for comparison, is the potential for the interaction of one CO 2 molecule and one carbon atom. It is important to note how the effect of the wall acts to deepen the well as compared with the case of two isolated particles. This extended well minimum is around -520 K or around 1.7 times transnational energies at 298 K, whereas the lone CO 2 -C minimum is at around -81 K. This result suggests why, on an energetic basis, a certain number of CO 2 molecules become trapped in this outer layer. The dimensions for this band agree well with the location for the first layer of high density CO 2 within the nanopore as predicted by the MD simulations of Skoulidas et al. at 1.0 bar. This situation is further visualized by the density plot shown in Fig. . Here the blue region indicates the low potential region for CO 2 -carbon while the red show the repulsive area. The inner area of near zero potential is given by the yellow region. It stands to reason that at low pressures, say 1.0 bar, the low potential region fills while the yellow and red regions remain vacant. However, as pressure is increased, the zero potential central region easily fills while the outer repulsive/exclusion band remains intact. The derivation for the potential, carried out above, assumes only an influence from the wall atoms in a ring bordering the plane which contains the CO 2 molecule. for improved accuracy, we now consider contributions to the potential from other wall atoms in an infinite tube. We assume the net influence on a CO 2 molecule due to all wall atoms in the tube can be approximated by considering a series of equally spaced identical rings of carbon atoms each of linear density A and with axial spacing 6 √ 2σ c , where σ C denotes the LJ parameter for carbon. In this case, d, originally given by Eq. ( ), becomes