Ab initio studies of effect of intercalation on the properties of single walled carbon and gallium phosphide nanotubes

We study and compare the geometric and electronic structures of sub-nanometer sized single walled nanotubes (NT) made of carbon (SWCNT) and gallium phosphide (SWGaPNT), with chirality index (10,0), using all electron based density functional theory calculations. We observe strong buckling effect in the optimized geometric structure of SWGaPNT due to the presence of mixture of sp2 and sp3 hybridizations. The buckling length is found to be about 0.48 Å. Our calculations show that both SWCNT(10,0) and SWGaPNT(10,0) are semiconductors with direct band gaps of 0.83 and 1.48 eV, respectively. Notably, this is in contrast to the respective bulk materials, which are semiconductors with indirect band gaps. We observe that with intercalation of alkali metal atom clusters (number of sodium atoms in unit cell varying from 1 to 4) in these tubes, there is a semiconductor to metal transition due to significant amount of charge transfer from valence band of sodium to the unoccupied bands of NTs. On the other hand, our spin-polarized calculations of these NTs intercalated with chains of single transition metal (TM) atom indicate that SWCNT(10,0) undergoes a transition from semiconducting to a half-metallic state and a signature of similar transition is observed for SWGaPNT(10,0) as well. On the contrary, the electronic structures of these nanotubes show metallicity when they are intercalated with more number of TM atoms.