First principles calculation of field emission from nanostructures using time-dependent density functional theory: A simplified approach

We introduce a new simplified method for computing the electron field emission current in short carbon nanotubes and graphene sheets using ab-initio computation in slab-periodic simulation cells. The evolution of the wave functions using Time-Dependent Density Functional Theory is computed by utilizing the Crank–Nicholson propagator and using the Octopus code (Castro et al., 2006 [1]), where we skip the wave function relaxation step elaborated by Han et al. (2002) [2], and apply a norm-conserving wave propagation method instead of the norm-nonconserving seventh-order Taylor Expansion method used by Araidai et al. (2004) [3]. Our method is mainly geared towards reducing the time it takes to compute the wave function propagation and enhancing the calculation precision. We found that in pristine carbon nanotubes, the emitted charge tends to emerge mostly from electrons that are concentrated at the nanotube tip region. The charge beam concentrates into specific channel structures, showing the utility of carbon nanotubes in precision emission applications.