Multi-scale approach to first-principles electron transport beyond 100 nm

Abstract

Multi-scale computational approaches are important for studies of novel, low-dimensional electronic devices since they are able to capture the different length-scales involved in the device operation, and at the same time describe critical parts such as surfaces, defects, interfaces, gates, and applied bias, on a atomistic, quantum-chemical level. Here we present a multi-scale method which enables calculations of electronic currents in two-dimensional devices larger than 100 nm 2 , where multiple perturbed regions described by density functional theory (DFT) are embedded into an extended unperturbed region described by a DFT-parametrized tight-binding model. We explain the details of the method, provide examples, and point out the main challenges regarding its practical implementation. Finally we apply it to study current propagation in pristine, defected and nanoporous graphene devices, injected by chemically accurate contacts simulating scanning tunneling microscopy probes. arXiv:1812.08054v2 [cond-mat.mes-hall]

Ab-initio wave packet dynamical simulation of defects in 2D materials

“…Firstly, in the case of the unperturbed graphene surface, we can see an anisotropic (hexagonal) spreading of the WP. This is in agreement with our earlier calculations [4], where the initial WP was injected onto the graphene surface from an STM tip and also with TB-DFT calculations in [15]. Secondly, an atomic scale modulation is present on the WP.…”

Removing all periodic boundary conditions: Efficient nonequilibrium Green's function calculations

“…In both graphs we find a discontinuity at 0.45 eV for the 3-electrode simulation (non existing in the real-space method) which we attribute to periodic image interaction. This fact is supported by other work [37] as well as it matches the bias on the tip.…”

Quantum Interference Engineering of Nanoporous Graphene for Carbon Nanocircuitry

“…Structural optimization is performed using a force threshold of 0.01 eV/Å. The parameters for the TB models are obtained directly from the converged DFT Hamiltonian and overlap matrices 31 and correspond to all on-site and coupling elements associated with the carbon p z orbitals for the planar NPG structures, and s, p x , p y and p z orbitals for the non-planar NPG structures. This model, obtained using the Pythonbased SISL utility, 18 retains the interaction range of the DFT basis set, is non-orthogonal, and takes the selfconsistent effects of the hydrogen passivation into ac-count.…”