Many-electron scattering applied to atomic point contacts

Abstract

Electron transport in a strong coupling regime is investigated by applying the many-electron correlated scattering (MECS) method to an atomic point contact model. Comparing the theoretical calculations to the quantum of conductance obtained experimentally for these systems allows for the error associated with the numerical implementation of the MECS method to be estimated and attributed to different components of the calculations. Errors associated with implementing the scattering boundary conditions and determination of the applied voltage in a finite explicit electrode model are assessed, and as well the impact on the basis set description on predicting the conductance is examined in this weakly correlated limit. The MECS calculation for the atomic point contact results in a conductance of 0.6G(0), in reasonable agreement with measurements for gold point contacts where approximately the conductance quantum G(0) is obtained. The analysis indicates the error attributable to numerical approximations and the explicit electrode model introduced in the calculations should not exceed 40% of the total conductance, whereas the effect of electron-electron correlations, even in this weakly correlated regime, can result in as much as a 30% change in the predicted conductance.

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

“…Herein many-electron correlated scattering (MECS) [17][18][19] is applied which relies on a many-electron wavefunction method, configuration interaction (CI), to calculate a 1e-RDM subject to open system boundary conditions. Previously, MECS has been applied to single MTJs consisting of benzene dithiol [17,18], alkane dithiol [25], alkane diamine [26], silane dithiol/diamine [27], and point contacts [28]. These calculations demonstrate that MECS predicts electronic currents consistent with measured molecular conductance.…”

“…[11]. Similar electrode structures have been studied in detail for the calculation of the conductance quantum in point contacts using the MECS approach [28]. For MECS calculations, a CI expansion is used to determine a many-electron wavefunction.…”

“…The limitations of the finite cluster approximation and extending the electrodes is considered in detail in ref. [28]. Using the same bond lengths and bond angles for the electrode tip and linker molecules as reported by Quek et al, the gold-BDA-gold MTJ is constructed and taken as a starting geometry.…”

“…Due the uncertainty principle, the Wigner phase-space distribution is not a true probability distribution function as it is not everywhere positive nor is it a unique phase space representation for quantum mechanics [24,38,39]. Nonetheless, in many cases the Wigner function is known to provide a semi-classical picture for electron distributions and this has been previously demonstrated for semiconductor devices and for the metal electrodes used in break junction experiments [28]. For MECS calculations, a plane normal to the current flow in each electrode is chosen and the Wigner function is averaged over this plane to give a one-dimensional representation of the momentum flowing across the plane.…”

“…In order for the assumption that the incoming electron momentum distributions at the Wigner planes remain in equilibrium with the fictional electron reservoirs, the Wigner planes need to be positioned within the finite electrode model at a position that minimizes edge effects [28]. Consideration of the placement of the Wigner planes focuses on the region in the electrodes between 7.5 and 9.5 a.u.…”