DFT-Based Molecular Transport Implementation in ADF/BAND

Abstract

We present a novel implementation of the first-principles approach to molecular charge transport using the nonequilibrium Green's function formalism in combination with the ADF/ BAND periodic band-structure DFT code, together with results for several example systems. As a proof of concept, we first discuss transport calculations on 1D chains of Li and Al atoms. We then present a detailed study of BDT and archetypal molecular wires from the OPE-family, sandwiched between 3D Au contacts, comparing well with results from the literature. Our implementation further allows us to make a comparison of 3D contacts with and without periodic boundary conditions, the latter being particularly useful for modeling the needle-shaped contacts used in break-junction experiments.

Applicability of the wide-band limit in DFT-based molecular transport calculations

“…For technical reasons, a Full-SCF calculation contains 90 Au atoms. 16 Finally, in the WBL-Molecule approach, the WBL self-energies are coupled directly to the p z orbital on the thiols or amines, which our studies indicate to be the dominant charge-injection pathway into the molecular system.…”

“…However, with WBL-Metal care must be taken when modeling junctions using 1D or 2D electrodes (such as carbon nanotubes 34,35 or graphene 36 ), and more generally for electrodes with a more complicated electronic structure near the Fermi energy. package, [12][13][14][15][16] using the LDA exchange-correlation potential. 55 A single-ζ (SZ) basis-set was used for the electrodes, and a triple-ζ polarized (TZP) basis-set was used for the molecule, although we find similar results with a DZP basis.…”

“…3, see Appendix A for details). In order to approximate the geometric configuration of single-molecule break-junction experiments, we do not employ periodic boundary conditions (PBCs), which would mimic a bulk substrate, but rather use needle-like ("non-PBC") electrodes, or wires 16 (with a 3 × 3 atom crosssection, see Fig. 3).…”

“…This transmission is typical for BDT calculations in the literature. 6,7,16,26,50 The red line shows the Post-SCF result, where the HOMO-LUMO gap is the same, but the peaks are slightly broadened with respect to the Full-SCF calculation. Also, the transmission is more "noisy," especially in the HOMO-LUMO gap.…”

“…[1][2][3][4] A number of codes [5][6][7][8][9][10][11] have been developed, including our own implementation within the Amsterdam Density Functional (ADF)/BAND quantum chemistry package. [12][13][14][15][16] As the methods have matured, scalability and the computational effort involved in studying progressively larger molecular systems have become important issues. In recent years, the focus of the field has shifted towards systems where the molecule predominantly determines the transport properties, rather than the metal-molecule interface.…”