Bandgaps of zigzag finite-length nanotubes ab initio calculations: ground state degeneracy and single-electron spectra

摘要

Different versions of ab initio quantum chemical models (cluster and periodic boundary conditions approximations) have been used to analyze the effect of finite length and the partial filling of the highest occupied orbital on the band-gaps of carbon nanotubes. In agreement with the previous calculations in the tight-binding approximation and pi-electron open shell model, it has been shown that the ground state of the nanotube with the zigzag structure is triplet. It has been confirmed that these tubes exhibit metallic or semiconductor properties with a very narrow half-filled conduction band. The band-gap is of order few tens of eV, and it is estimated that approximately 0.1-0.2% of pi-electrons belong to the conduction band of finite zigzag nanotubes. The triplet state is predicted to be the ground state of finite-length carbon nanotubes.