  The evolution of electronic wave packets (WPs) through grain boundaries (GBs)
of various structures in graphene was investigated by the numerical solution of
the time-dependent Schroedinger equation. WPs were injected from a simulated
STM tip placed above one of the grains. Electronic structure of the GBs was
calculated by ab-initio and tight-binding methods. Two main factors governing
the energy dependence of the transport have been identified: the misorientation
angle of the two adjacent graphene grains and the atomic structure of the GB.
In case of an ordered GB made of a periodic repetition of pentagon-heptagon
pairs, it was found that the transport at high and low energies is mainly
determined by the misorientation angle, but the transport around the Fermi
energy is correlated with the electronic structure of the GB. A particular line
defect with zero misorientation angle (Lahiri et al, Nat Nanotechnol
2010,5:326) behaves as a metallic nanowire and shows electron-hole asymmetry
for hot electrons or holes. To generate disordered GBs, found experimentally in
CVD graphene samples, a Monte-Carlo-like procedure has been developed. Results
show a reduced transport for the disordered GBs, primarily attributed to
electronic localized states caused by C atoms with only two covalent bonds.
