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

A systematic study of type 1 armchair double-walled SiC nanotubes (DWNTs) ( n , n ) @ ( m , m ) ( 3 ≤ n ≤ 6 ; 7 ≤ m ≤ 12 ) using the finite cluster approximation is presented. The geometries of the tubes have been spin optimized using the hybrid functional B3LYP (Becke’s three-parameter exchange functional and the Lee–Yang–Parr correlation functional) and the all-electron 3-21G* basis set. The study indicates that the stabilities of the double-walled SiC nanotubes are of the same order as those of single-walled SiC nanotubes suggesting the possibilities of experimental synthesis of both single-walled and double-walled SiC nanotubes. The binding energy per atom or the cohesive energy of the double-walled nanotubes depends not only on the number of atoms but also on the coupling of the constituent single-walled nanotubes. The formation energy of the DWNTs is found to be maximum when the interlayer separation is about 3.5 Å. The DWNTs ( n , n ) @ ( n + 4 , n + 4 ) are found to have large formation energies. In particular, (5,5)@(9,9) DWNT is the most stable tube in our study with a binding energy per atom of 5.07 eV, the largest formation energy of 12.39 eV, an interlayer separation of 3.58 Å and a “band gap” of 1.97 eV. All double-walled SiC nanotubes are found to be semiconductors, with the band gaps decreasing from single-walled nanotubes to double-walled nanotubes.