Electrode-molecule energy level offsets in a gold-benzene diamine-gold single molecule tunnel junction

Abstract

One means for describing electron transport across single molecule tunnel junctions (MTJs) is to use density functional theory (DFT) in conjunction with a nonequilibrium Green's function (NEGF) formalism. This description relies on interpreting solutions to the Kohn-Sham (KS) equations used to solve the DFT problem as quasiparticle (QP) states. Many practical DFT implementations suffer from electron self-interaction errors and an inability to treat charge image potentials for molecules near metal surfaces. For MTJs, the overall effect of these errors is typically manifested as an overestimation of electronic currents. Correcting KS energies for self-interaction and image potential errors results in MTJ current-voltage characteristics in close agreement with measured currents. An alternative transport approach foregoes a QP picture and solves for a many-electron wavefunction on the MTJ subject to open system boundary conditions. It is demonstrated that this many-electron method provides similar results to the corrected QP picture for electronic current.Analysis of these two distinct approaches are related through corrections to a junction's electronic structure beyond the KS energies for the case of a benzene diamine molecule bonded between two gold electrodes.

Conductance Switching in an Organometallic Single-Electron Transistor Using Current-Constrained Reduced-Density Matrix Theory

“…Our approach is similar in spirit to the many-electron correlated scattering (MECS) formalism which constructs the 1-RDM from a full CI wave function through a constrained minimization and, hence, affords a many-body picture of electron transport. The latter formalism has been shown to be extremely successful on a variety of systems in the past , and has recently even been demonstrated to attain excellent agreement with experiment and with the self-interaction error corrected version of DFT-NEGF by Quek et al Unlike the MECS formalism, our method variationally obtains the 1-RDM directly from a constrained semidefinite optimization scheme on the two-particle reduced density matrix (2-RDM).…”

A multiconfigurational pair-density functional theory approach to molecular junctions

“…22 To the authors' knowledge, none are yet in widespread use even though interest in other multireference transport methods such as multilayer multiconfiguration time-dependent Hartree method, time-dependent reduced density matrix theories, and time-dependent CI theories is growing rapidly. 9,[23][24][25][26][27][28][29] This is likely due, at least in part, to the computational cost of using a CI wavefunction to construct the Green's function directly. This cost can be mitigated if an active space approach is employed, such as the complete active space self-consistent field (CASSCF) method.…”