Achieving Predictive Description of Molecular Conductance by Using a Range-Separated Hybrid Functional

Abstract

The conductance of molecular bridges tends to be overestimated by computational studies in comparison to measured values. While this well-established trend may be related to difficulties for achieving robust bridges, the employed computational scheme can also contribute to this tendency. In particular, caveats of the traditional functionals employed in first-principles-based calculations can lead to discrepancies reflected in exaggerated conductance. Here, we show that by employing a range-separated hybrid functional the calculated values are within the same order as the measured conductance for all four considered cases. On the other hand, with B3LYP, which is a widely used functional, the calculated values greatly overestimate the conductance (by about 1-2 orders of magnitude). The improved description of the conductance with a RSH functional builds on achieving a physically meaningful treatment of the quasi particles associated with the frontier orbitals.

Achieving Predictive Description of Negative Differential Resistance in Molecular Junctions Using a Range‐Separated Hybrid Functional

“…[ 36–39 ] We have reported use of RSH within the Landauer picture that achieves impressive success in calculating conductance of thiol gold‐anchored molecular junctions. [ 40 ] The RSH‐calculated conductances are found to be within the order of magnitude as of the measured values for four considered benchmark systems, whereas B3LYP values (or other previously reported calculations) overestimate the conductance by one to two orders of magnitude. The observed trend clearly results from the success of RSH functionals to properly open up the fundamental orbital gap associating the frontier orbitals to energies of adding and removing an electron, therefore avoiding the tendency of traditional functionals to collapse the gap.…”

“…In this way, our NDR study harvests the success in addressing conductance at the zero bias limit. [ 40 ] We contrast the RSH‐NEGF level to alternative combinations of DFT‐NEGF employing LDA or a hybrid functional by validating against measurements finding NDR in nitro‐substituted OPE. [ 13 ] The second goal is to gain fundamental insight explaining the origin of the NDR.…”

Current-constrained density-matrix theory to calculate molecular conductivity with increased accuracy

“…All three of these methods yield currents that are 1-2 orders of magnitude larger than those from the experiment. It is well-known that DFT with NEGF tends to overpredict the conductance by a significant amount, potentially orders of magnitude [18][19][20][21][22] . The overprediction has been attributed to several factors including the energetic positioning of the Kohn-Sham orbitals.…”

“…Although these methods have been successful in predicting molecular conductivity, limitations exist in their quantitative accuracy from variability in (1) their establishment of voltage through a chemical potential and (2) their treatment of electron correlation in the context of transport. The approximation of the nonequilibrium Greens functions method with density functional theory (NEGFT-DFT) is known to overpredict the current in some benchmark molecules by as much as an order of magnitude [18][19][20][21][22][23] . Here, we propose a new theory of molecular conductivity that uses a current-constrained variational principle based on two-electron reduced density matrices (2-RDMs) to address these limitations.…”

Energy level alignment at molecule-metal interfaces from an optimally tuned range-separated hybrid functional

“…OT-RSH was shown to yield accurate frontier orbital energy levels, outer-valence electron spectra, and HOMO-LUMO gaps of gas-phase molecules [81][82][83][84][85][86][87][88][89] and molecular crystals, 90,91 as well as transport properties. 92,93 In this work, we extend the applicability of this functional to heterogeneous molecule-metal interfaces by proposing a route for a judicious choice of optimal parameters in the OT-RSH functional. This yields a fully self-consistent OT-RSH scheme which is applicable to both physisorbed and chemisorbed molecule-metal systems and thus extends methods reliant on the weak coupling limit.…”