Hydrogen interaction with single-walled carbon nanotubes: A combined quantum-mechanics/molecular-mechanics study

A mixed quantum mechanics/molecular mechanics (QM/MM) model is used for investigating the nature of hydrogen adsorption in single-walled carbon nanotubes (SWNTs). For the QM part the B3LYP functional was used while for the MM we employ the universal force field (UFF). Our model includes up to 64 carbon and 32 hydrogen atoms in the OM region and up to 200 carbon atoms of a (4,4) SWNT in the MM region. Our results demonstrate that hydrogen atoms will bind to the tube walls and not enter in the tube interior. This binding will take place in zigzag rings around the tube walls and not in lines toward the tube axis, changing the tube shape and causing an enlargement of the tube volume by 15%. After the tube walls are half-filled with hydrogens, we obtained the energetically more favorable procedure of hydrogen insertion in the tube.