Ghost atoms are supposed to correct for wave function tail in the vacuum region, because the localized basis functions are short-range in QuantumATK. The ghost atoms provide atomic orbitals in the vacuum that can accommodate some charge. This charge decay quickly into the vacuum region.
Since the ghost atoms are in the vacuum, they give some correction to quantum, coherent tunneling of charge carriers through the vacuum spacer.
Having the ghost atoms has nothing to do with hopping mechanism for the electron transport.
