Invited talk

N≥1 NEGF calculations & molecular projected transport

N. Papior^1,2

¹Catalan Institute of Nanoscience Nanotechnology, Campus UAB, Bellaterra, Spain

²Center for Nanostructured Graphene (CNG), DTU Nanotech, DTU, Denmark

I will present the recent development of N≥1 electrode NEGF simulations which enables simulations of multiprobe physics. The specific implementation will be presented [1,2] and the efficiency and scalability of the code (TranSIESTA) will be emphasized. The code implements hybrid parallelization which easily enables efficient calculations of systems with more than 10,000 orbitals under non-equilibrium, see Fig. 1 which shows the maximum memory usage with respect to system size (x-axis) and electrode size (y-axis), left. The right shows the computation time of a single SCF with NEGF. Using the N electrode capability I will present initial 3 terminal results based on a 2D-graphene interconnects [3].

After having introduced the NEGF method I expand on the transmission calculations where I will focus on projected molecular transport, see Fig. 2. Projections enable spectroscopy of molecular eigenstates and the identification of the electron carrying pathways. They will provide an intuitive understanding of the physics governing the transport properties of the junction. I will analyze the transport projection of the C₆₀ molecule in a close packed Cu surface [4]. Importantly the projection is not limited to molecules and it will be shown that a generic projection onto k-resolved eigenstates is also possible.

Fig. 1: Memory/Time use of 2-terminal NEGF calculations.

Fig. 2: Transmission projection of molecule eigenstates.

[1] Papior, PhD thesis (2016).

[2] Papior et al. (to be submitted).

[3] Jacobsen et al., Carbon 101, 101-106 (2016).

[4] Schneider et al., Journal of Physics Condensed Matter 27, 015001 (2014).