  While the Landauer viewpoint constitutes a modern basis to understand
nanoscale electronic transport and to realize first-principles implementations
of the non-equilibrium Green's function (NEGF) formalism, seeking an
alternative picture could be beneficial for the fundamental understanding and
practical calculations of quantum transport processes. Herein, introducing a
micro-canonical picture that maps the finite-bias quantum transport process to
a drain-to-source or multi-electrode optical excitation, the multi-space
constrained-search density functional theory (MS-DFT) formalism for
first-principles electronic structure and quantum transport calculations is
developed. Performing MS-DFT calculations for the benzenedithiolate
single-molecule junction, it is shown that MS-DFT and standard DFT-NEGF
calculations produce practically equivalent electronic and transmission data.
Importantly, the variational convergence of "non-equilibrium total energy"
within MS-DFT is demonstrated, which should have significant implications for
in operando studies of nanoscale devices. Establishing a viable alternative to
the Landauer viewpoint, the developed formalism should provide valuable
atomistic information in the development of next-generation nanodevices.

Mesoscale and Nanoscale Physics