Molecular conductance calculations of single-molecule junctions using projection-based density functional embedding

Single-Molecule Junctions (SMJs) are key platforms for the exploration of electron transport at the molecular scale. In this study, we present a method that employs different exchange-correlation density functionals for the molecule and the lead domains in an SMJ, enabling the selection of the optimal one for each part. This is accomplished using a formally exact projection-based density-functional theory (DFT-in-DFT) embedding technique combined with the non-equilibrium Green's function method to predict zero-bias conductance. The effectiveness of this approach is illustrated through transport calculations on SMJs with benzene-1,4-diamine and its tetramethylated and tetrafluorinated variants, using the CAM-B3LYP range-separated hybrid functional for the embedded molecule and the Perdew-Burke-Ernzerhof (PBE) functional for the electrodes. The findings indicate a substantial improvement in the accuracy of the predicted zero-bias conductance compared to traditional modeling using the PBE functional across the entire system. The causes for the noted improvement are demonstrated through the examination of alterations in the energy levels of the embedded molecule, along with variations in the electrode-molecule interactions.