A density functional theory (DFT) study of purified single-wall carbon nanotube (SWCNT) molecular models has shown that open-ended carboxylated C(10,0) and C(5,5) are more acidic than benzoic acid, but moreover, that C(10,0)-COOH is slightly more acidic than C(5,5)-COOH, possibly enabling separation by chirality. In addition, an increase in the ionization potential may indicate a suppression of field emission for purified SWCNTs. Finally, we address the complexity of the large-scale DFT calculations by the application of the same level of theory but with a different basis set (SLDB) method, shown to be advantageous as compared to ONIOM. (c) 2006 Elsevier B.V. All rights reserved.