Tunneling electronic currents simulated with localized basis sets

Abstract

The description of tunneling currents from non-equilibrium electronic structure using localized basis sets is very demanding. The problem stems from the lack of accuracy to describe evanescent waves in the tunneling barrier when the basis set is limited. The same problem exists for extended basis sets such as planewaves, except because increasing the number of planewaves simply improves the description. With local basis sets several strategies exist for improving the tunneling scattering structure. Here, we explore them and compare with previous work. Our conclusion is that using ghost atoms in self-consistent codes such as Transiestais a valid and accurate way of performing tunneling calculations. However, attention must be paid not to break the symmetry of the transmission channels by incorrect inclusion of the ghost atom and to perform a fully self-consistent calculation to avoid ghost transmissions.