Electronic structure of C60-encapsulating semiconducting carbon nanotube

The electronic structure of a C60-encapsulating (14,7) carbon nanotube is studied by the local density approximation (LDA) in density-functional theory. The (14,7) nanotube is a semiconductor with the LDA gap of 0.5 eV. On the other hand, its fullerene-encapsulating form is a narrow-gap semiconductor with the LDA gap of only 0.2 eV. The top of the valence band has a nanotube-character, while the bottom of the conduction band is the C60 t1u band, because of descent of the C60-origin bands upon the encapsulation into the nanotube. Analysis of the charge distribution indicates that the descent of the C60 bands is due to hybridization with the nearly free-electron state of the nanotube.