Spin-polarized electron transport through nanojunctions

The conductance properties of nanojunctions connected to macroscopic electrodes can be explored through quantum transport calculations that employ non-equilibrium Green's functions (NEGF) alongside density functional theory (DFT). When these systems exhibit electron spin polarization, the theoretical analysis often incorporates spin-polarized or unrestricted DFT. In this contribution, we present several examples of nanostructures where this approach has proven effective. First, we examine spin-polarized currents in zigzag graphene nanoribbons (zGNRs) subjected to electric fields and finite bias voltages.[1] Next, we explore electron transport through molecules with unpaired electrons, in particular oxidized molecules that demonstrate highly conductive low-energy states, classified as one-dimensional topological insulators.[2] It is well-known that DFT can encounter difficulties with open-shell structures due to their multiconfigurational nature. We illustrate how a selection of polycyclic aromatic hydrocarbons— such as those previously studied in recent scanning probe experiments [3]—can have their ground state accurately determined using a multi- configurational short-range DFT approach.[4] Our findings underscore both the effectiveness and the limitations of integrating DFT with NEGF calculations.