Multi‐Space Excitation as an Alternative to the Landauer Picture for Nonequilibrium Quantum Transport

While the Landauer viewpoint constitutes a modern basis to understand nanoscale electronic transport and to realize first‐principles implementations of the nonequilibrium Green's function (NEGF) formalism, seeking an alternative picture can 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 “nonequilibrium 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.