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In this paper, the heterofullerenes made of the smallest fullerene, C20were investigated by quantum chemistry calculations based on density functional theory. The geometrical structures, energies, electronic properties, and the aromaticities of the C19X (X = B, N, O, Al, Si, P, S, Ga, Ge, As, and Se) cages were studied systemically and compared with those of the pristine C20cage. It is found that the doped cages with different heteroatoms exhibit various structural, electronic, and aromatic properties. Several doping behaviors of the C19X cages are different from those of the C59X cages. These results imply the possibility to modulate the physical properties of heterofullerenes by tuning the sizes of the carbon cages as well as the substitution elements. [ABSTRACT FROM PUBLISHER]

Boron nitride nanotubes (BNNTs) are semiconductors with a wide band gap. In comparison with carbon nanotubes (CNTs), BNNTs have higher chemical stability, excellent mechanical properties and higher thermal conductivity. In this paper, we study the effect of diameters and substituting B and N atoms of various zigzag BNNTs with Al, on structural and electronic properties of BNNTs in solid state using the density functional theory method. The results of calculations of density of states and band structure (band) showed that the band gap between the valence and conduction level increases as a result of the enhancement of tube diameter of BNNTs. Finally, the results showed that the electronic properties of the pristine BNNTs can be improved by doping Al atom in the zigzag configuration of tubes. [ABSTRACT FROM AUTHOR]

The geometries, growth patterns, relative stabilities and electronic properties of small-sized Pd2Sinand Sin+2(n= 1–11) clusters are systematically studied using the hybrid density functional theory method B3LYP. The optimised structures revealed that the lowest energy Pd2Sinclusters are not similar to those of pure Sinclusters. Whenn= 9, one Pd atom in Pd2Si9completely falls into the centre of the Si outer frame, forming metal-encapsulated Si cages. On the basis of the optimised structures, the averaged binding energy, fragmentation energy, second-order energy difference and highest occupied–lowest unoccupied molecular orbital energy gap are calculated. It is found that the Pd2Si5and Pd2Si7clusters have stronger relative stabilities among the Pd2Sinclusters. Additionally, the stabilities of Sin+2clusters have been reduced by the doping of Pd impurity. The natural population and natural electronic configuration analysis indicated that the Pd atoms possess negative charges forn= 1–11 and there exist the spd hybridisation in the Pd atom. Finally, the chemical hardness, chemical potential, electrostatic potential and polarisability are discussed. [ABSTRACT FROM PUBLISHER]