  The current carried by a material subject to an electric field is
microscopically inhomogeneous and can be modelled using scattering theory, in
which electrons undergo collisions with the microscopic objects they encounter.
We herein present a methodology for parameter-free calculations of the current
density from first-principles using Density Functional Theory, Wannier
functions and scattering matrices. The methodology is used on free-standing
AB-stacked bilayer penta-silicene. This new Si allotrope has been proposed to
have a higher stability than any of its hexagonal bilayer counterparts.
Furthermore, its semiconducting properties make it ideal for use in electronic
components. We unveil the role of the pz orbitals in the transport through a
three-dimensional quantum wire and present current density streamlines that
reveal the locations of the highest charge flow. The present methodology can be
expanded to accommodate many electron degrees of freedom, the application of
electromagnetic fields and many other physical phenomena involved in device
operation.
