For a two-probe system, the periodicity in the x and y directions is included by default. The conductor in the scattering region can be a molecule or a part of bulk materials. For the latter case, one may do the following ways:
i). choose a suitable plane of bulk material and cleave it to make a slab. Here one should be take care about the lattice match problem. That is to say, the cross area (i.e., x and y directions) of scattering region should be same to the one of electrodes.
ii). prepare the xyz file for the created slab.
iii). import the xyz file and add it to the two-probe system. This is very similar to the construction of a two-probe system with molecule in the scattering region.
