Alkali-earth metal adsorption behaviors on capped single-walled carbon nanotubes based on first-principle calculations

The adsorption behaviors of alkali-earth metals (AEMs) on the capped (5, 5) and (9, 0) carbon nanotubes (CNTs) are investigated using first-principle calculations based on generalized gradient approximation. The optimized geometry, adsorption energy, induced dipole moment, and work function, at two different sites like hexagon and pentagon, of each adatom-CNT system are calculated. The decrease of work functions, variations of Fermi levels and Bader charge transfer, in spite of CNT chirality, has almost the same regularity when the AEMs are adsorbed on the same polygon. The AEMs are off the pentagonal center of the CNTs, while for the hexagon of the CNTs, their most preferred sites are just the top of the rings. In particular, the adsorption energy and work function reduction of the AEMs on hexagon are slightly larger than that on pentagon.

When alkali-earth metals are adsorbed on the two sites of capped CNTs, the work function line slop of AEMs adsorbed on (5, 5) CNTs' pentagon parallel to that of AEMs adsorbed on (9, 0) CNTs' pentagon without depending on chirality. The AEMs on CNTs' hexagon systems have similar characteristics. Finally, the work function line slop of AEMs adsorbed on CNTs' hexagon is 2.2 and agrees more with Gordy–Thomas equation, while the work function line slop of the AEMs adsorbed on pentagon is 1.7, which is less than that of hexagon. The variations in the vacuum levels increase linearly as the induced dipole moments increase from P1 to P3.Figure optionsDownload as PowerPoint slideHighlights
► Behaviors of metal adsorption on pentagon or hexagon of CNTs vary to some extent.
► There is a linear relationship between Fermi level of CNTs and electronegativity.
► Fermi levels and Bader charge transfer are to do with polygon of capped CNTs.
► Adsorption energy of AEMs on hexagon is slightly larger than that on pentagon.
► Work function reduction of AEMs on hexagon is slightly larger than that on pentagon.