(a) Total valence electron charge density plot. The value of charge contour is 0.0015 (el/Å3) showing the binding charge between the SWNT and the NO2 molecule. Three units are shown in this figure. (b) Binding energy curve for NO2 interacting with SWNT as a function of distance from NO2 to the nanotube. The solid line curve is a fitting with universal binding curve [31].
