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Self-consistent tight binding model adapted for hydrocarbon systems

A self-consistent environment-dependent tight binding method is presented that was developed to simulate eigenvalue spectra, electron densities and Coulomb potential distributions for hydrocarbon systems. The method builds on a non-self-consistent environment-dependent tight binding model for carbon [Tang et al., Phys. Rev. B 53, 979 (1996)] with parameters added to describe hydrocarbon bonds and to account for self-consistent charge transfer. A detailed description of the parameterization procedure is given. Case studies that examine electron emission-related properties of carbon nanotubes demonstrate the utility of the method. The results of these calculations indicate that field enhancement in the vicinity of a nanotube tip is higher for open-ended than for capped nanotubes. At the same time open-ended nanotubes exhibit a higher potential barrier in the tip region. This barrier deteriorates the coupling between conducting states in the nanotube and free electron states in vacuum, and may increase the field emission threshold.