Platinum atomic contacts: From tunneling to contact

We present a theoretical study of the electronic transport through Pt nanocontacts. We show that the analysis of the tunneling regime requires a very careful treatment of the technical details. For instance, an insufficient size of the system can cause unphysical charge oscillations to arise along the transport direction; moreover, the use of an inappropriate basis set can deviate the distance dependence of the conductance from the expected exponential trend. While the conductance decay can be either corrected by employing ghost atoms or a large-cutoff-radius basis set, the same does not apply to the corrugation, for which only the second option is recommended. Interestingly, these details were not found to have a remarkable impact in the contact regime. These findings are important for theoretical studies of distance-dependent phenomena in scanning-probe and break-junction experiments.

Figure 1

Geometry used to analyze the Mulliken charges in the $3\text{−}6\text{−}3$ system of Fig. 2. The vertical black lines separate the central (C), left (L), and right (R) region.

Figure 2

Mulliken population with (left) $s1p1d1$ and (right) $s2p2d1$ basis set in systems $l\text{−}c\text{−}r$, where $l\left(r\right)$ and $c$ indicate the number of layers in each lead and in the central part, respectively. The following combinations are shown: 3-6-3 (a), 3-9-3 (b), 3-12-3 (c), 6-6-6 (d), 6-9-6 (e). The vertical dashed green light indicates the 5 Å separation.

Figure 3

Transmission as a function of energy for the $s2p2d1$ systems (a)–(e) of the right panels in Fig. 2.

Figure 4

$ln$ of the conductance obtained throughout the stretching process of the junctions, starting from a hollow and a top binding configuration, for three different cutoff radii as well as by making use of ghost atoms.

Figure 5

Conductance in top and hollow geometry (solid lines) and corresponding interpolation (dashed lines) for three different cutoff radii and for the insertion of ghost atoms. In the inset, the corrugation as a function of the separation distance is shown.

Figure 6

Transmission as a function of energy, for the geometry depicted in the inset, in four different cases: in the first two, either the $s1p1d1$ or the $s2p2d1$ basis set is used for both leads and central region; in the other two cases, the atoms in the tip and the innermost layer (on both sides) is described by either $s2p2d1$ or $s2p2d2$, while the rest is treated by the $s1p1d1$ set.

Figure 7

Comparison between the transmission curves obtained, for the geometry depicted in the inset of Fig. 6, by OpenMX with the $s1p1d1$ basis set, and by ANT with the CRENBS and Lanl2dz basis set.

Figure 8

NormRD throughout the scf convergence steps for the case in which the NEGF extension is switched on after 5000 steps (case 1, black curve) and only 3000 steps (case 2, green curve). Waiting for NormRD to reach a much lower value before switching to the NEGF method does not accelerate the convergence process.