Theoretical Study On The Interaction Between Carbon Nanostructures And Small Molecules

We applied density functional tight binding method with the empirical Londondispersion energy term （DFTB-D） to study the adsorption of small molecules ongraphene and carbon nanotubes（CNTs）.The adsorption of six free radicals （FRs） on a graphene fragment was studiedusing a density functional tight binding method with the inclusion of an empiricaldispersion term in total energy. The results indicate that the different interaction pathsbetween the FRs and the graphene lead to different forms of physical adsorption （PA）or chemical adsorption （CA）. The CA appears only in the condition where some ofthe non-hydrogen atoms are closer to the graphene, with the deformation occurring inthe latter. The charge transfer increases with the increase in adsorption energy inevery FR-graphene system. Whereas the deformation in the graphene is negligible inall PA cases, in all CA cases, the closer the FR is to the graphene, the clearer thegraphene deformation is, with all atomic displacements being larger than0.1. Ourfindings are useful not only for free radical scavenging, but also for studying theinteraction between general molecules and surfaces of meterials.We applied the DFTB-D method to study the binding of molecules H₂O, CH4,NH₃with four defective configurations which are likely to occur in （5,5） single wallcarbon nanotubes （SWCNT） comparing with a pure （5,5） SWCNT. Using a suitable DFTB method, we calculated the interaction including adsorption energy, chargetransfer, gap value and dipole moment between SWCNTs （with and without defect）and small molecules. Our calculations clearly indicate that physical adsorption is acommon case except that ammonia readily represents both PA and CA. Despite ofimmanent gap and dipole moment of the SWCNT are inconspicuously changed byadsorbing small molecules. But the energy of physical adsorption range is0-400meVbetween three small molecules and varies tubes. Comparing to the pure SWCNT, thecalculated results show that there are above200meV for the adsorption energybetween H₂O and two defective SWCNTs （a and d）, and explore a phenomenamarked charge transfer on the defective tube.