On the existence and stability of double-walled armchair silicon carbide nanotubes

► A systematic study of SiC nanotubes (n,n)@(m,m) (3≤n≤6;7≤m≤12). ► Geometries of tubes are optimized using the functional B3LYP and the 3-21G* basis. ► Formation energy is maximum when the interlayer separation is about 3.5 Å.► (5,5)@(9,9) is the most stable with B.E./atom and formation energy of 5.07 and 12.39 eV. ► All DWNTs are semiconductors, with band gaps decreasing from SWNTs to DWNTs.