DFT Calculations of Hydrogen Adsorption inside Single-Walled Carbon Nanotubes

Table 1

PBE-D3/SVP binding (E_b) and interaction energies (E_i) for endohedral complexes of hydrogen and SWCNTs (graphene). The equilibrium distances (R, Å) are normal between center of mass of a hydrogen molecule and a SWCNT (graphene). All energies are in eV.

System	Parallel orientation			Perpendicular orientation
	Eb	Ei	R^1	Eb	Ei	R
(3,3) SWCNT	1.906	2.048	2.00	2.149	2.360	2.00
(4,4) SWCNT	−0.057	−0.053	2.75	0.010	0.019	2.78
(5,5) SWCNT	−0.195	−0.187	3.05	−0.199	−0.200	3.28
(6,6) SWCNT	−0.135	−0.123	3.07	−0.141	−0.128	3.04
(7,7) SWCNT	−0.110	−0.071	3.06	−0.113	−0.074	3.05
(8,8) SWCNT	−0.077	−0.035	3.54	−0.076	−0.038	3.62
Graphene	−0.066	−0.067	3.10	—^2	−0.068	3.10

¹The equilibrium distances (R) are measured between an H₂ molecule and the closest wall of a SWCNT; ²for graphene, there is only one value of E_b as the initial parallel and perpendicular orientations converge to one equilibrium configuration.