Self-Interaction Errors in Density-Functional Calculations of Electronic Transport

All density-functional calculations of single-molecule transport to date have used continuous exchange-correlation approximations. The lack of derivative discontinuity in such calculations leads to the erroneous prediction of metallic transport for insulating molecules. A simple and computationally undemanding atomic self-interaction correction (SIC) opens conduction gaps in $I\mathrm{\text{−}}V$ characteristics that otherwise are predicted metallic, as in the case of the prototype $\mathrm{Au}/\mathrm{\text{ditholated-benzene}}/\mathrm{Au}$ junction.

Figure 1

(a) Schematic two terminal device. Two leads are kept at the chemical potentials ${\mu }_{\mathrm{L}}$ and ${\mu }_{\mathrm{R}}$ and the transport is through a single energy level $ϵ$. The hopping energy between the leads and the energy level is $\Gamma$. (b) Dependence of $ϵ$ on its own occupation $n$. The straight line corresponds to a typical LDA dependence and the steplike line to the DISC. Notice that the LDA line becomes flat at $n\sim 1.5$ [$ϵ(n)=0$] since here the eigenstate is unbound. The dotted horizontal line denotes the position of the leads Fermi level $E_{\mathrm{F}}$.

Figure 2

(a) Current $I$, (b) occupation $n$, and (c) position of the energy level $ϵ$ as a function of bias $V$. The parameters used here are $ϵ(0)=-5.5\mathrm{eV}$, $U=5\mathrm{eV}$, $E_{\mathrm{F}}=-5.0\mathrm{eV}$, and $T=300°\mathrm{K}$. The curves on the left-hand side are obtained in the weak coupling limit ($\Gamma =0.02\mathrm{eV}$) and those on the right-hand side in the strong coupling limit ($\Gamma =1.2\mathrm{eV}$).

Figure 3

BDT molecule attached to (001) oriented Au surfaces. The angle $\varphi$ between the BDT plane and the gold modulates the strength of the molecule/lead coupling.

Figure 4

(a) $I\mathrm{\text{−}}V$ characteristic, (b) occupation as a function of energy, and (c) DOS for the system $\mathrm{BDT}+\mathrm{Au}$ leads. The cases of strong ($\varphi =30°$) and weak coupling ($\varphi =5°$) are presented, respectively, in the right- and left-hand side panels. We present only LDA DOS, since PSIC gives almost identical results in the energy window shown here. In panels (c) the vertical lines denote the position of $E_{\mathrm{F}}$.