The Two-Layer ONIOM Technique in the Studies of Chemical Reactions on Carbon Nanotube Tips
V.A. Basiuk and E.V. Basiuk
Universidad Nacional Autonoma de Mexico, MX
Keywords: carbon nanotubes, chemical reactions, ONIOM, molecular mechanics, semi-empirical, DFT
In continuation of our combined quantum mechanics/molecular mechanics (QM/MM) studies of selective amidation (reaction 1) and esterification (reaction 2) of monocarboxy-substituted tips of zigzag and armchair single-walled carbon nanotube (SWNTs), we studied theoretically the interaction of simple aliphatic amines with carboxylated zigzag and armchair SWNT models. These reactions are extremely important in carbon nanotube derivatization, solubilization and purification. Our recent theoretical studies revealed energetic preferences of amide and ester formation on the armchair nanotubes as compared to their zigzag counterparts. In the present work, we used single-level MM+ molecular mechanics and AM1 semi-empirical method to study non-covalent interactions. To study reaction 1, the two-level ONIOM technique was employed where the higher level was treated with B3LYP/6-31G(d) DFT, and the lower level was described with either UFF molecular mechanics or AM1. Since we found that the use of AM1 for the lower-level description has serious limitations, to study theoretically chemical reactions on carbon nanotube tips with the ONIOM technique, where the higher level is treated with B3LYP density functional theory, we recommend UFF molecular mechanics versus AM1 semi-empirical method for the lower-level description.
Nanotech 2004 Conference Technical Program Abstract