In this article, we have performed calculations for studying the stability of carbon group elements, such as Si and Ge, and also magnetic elements, like Fe and Co, via first principle investigations. We found that Si and Ge decoupled from the interior surface of carbon nanotubes, this fact was independent in curvature, radius, conductivity and number of atoms in the carbon nanotubes. But the magnetic elements bonded to the surface of the tube via the electronegativity factor. The binding energy calculated for Co was -3.82 eV which is more stable than that of Fe (-2.65 eV) due to a lrger decrease in its magnetization. The magnetization of Fe and Co changed from 4.00 μB to 3.40 μB and 3.00 μB to 1.75μB , respectively. Finally, we came to the conclusion that carbon group elements are favorable for hydrogen absorption inside the carbon nanotube, whereas magnetic elements are suitable for hydrogen adsorption on the nanotube surface.

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