A multiscale theoretical approach is used for the investigation of hydrogen storage in silicon-carbon nanotubes (SiCNTs). First, ab initio calculations at the density functional level of theory (DFT) showed an increase of 20% in the binding energy of H2 in SiCNTs compared with pure carbon nanotubes (CNTs). This is explained by the alternative charges that exist in the SiCNT walls. Second, classical Monte Carlo simulation of nanotube bundles showed an even larger increase of the storage capacity in SiCNTs, especially in low temperature and high-pressure conditions. Our results verify in both theoretical levels that SiCNTs seem to be more suitable materials for hydrogen storage than pure CNTs.

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Combined ab initio and grand canonical Monte Carlo simulations have been performed to investigate the dependence of hydrogen storage in single-walled carbon nanotubes (SWCNTs) on both tube curvature and chirality. The ab initio calculations at the density functional level of theory can provide useful information about the nature of hydrogen adsorption in SWCNT selected sites and the binding under different curvatures and chiralities of the tube walls. Further to this, the grand canonical Monte Carlo atomistic simulation technique can model large-scale nanotube systems with different curvature and chiralities and reproduce their storage capacity by calculating the weight percentage of the adsorbed material (gravimetric density) under thermodynamic conditions of interest. The author's results have shown that with both computational techniques, the nanotube's curvature plays an important role in the storage process while the chirality of the tube plays none.

Grand canonical Monte Carlo (GCMC) simulations combined with ab initio QM calculations were employed to study the adsorption capacity of H 2 in single-walled silicon nanotubes (SWSiNTs) of a hypothetical armchair structural model. The interaction energy of H 2 with a graphite-like sheet from the surface of a single SiNT obtained from the QM calculations was fitted to an accurate potential function used to simulate the system. This theoretical approach is also used in SWCNTs of similar characteristics and at the same thermodynamic states. The GCMC simulation of NT bundles with H 2 showed enhancement of H 2 adsorptivity of SiNTs, as compared with CNTs. Concretely, the (14, 14) SWSiNTs present remarkable percentage improvement of 100, 70, 44, and 25% in the gravimetric (weight percent) adsorption of H 2 at 293 K and 0.1, 1.0, 5.0, and 10.0 MPa, respectively, as compared with isodiameter (22,22) CNTs. This is attributed to the stronger attractive interaction of H 2 with SiNTs as compared to CNTs, found from the first principle calculations.