Ab initiononequilibrium quantum transport and forces with the real-space projector augmented wave method

Abstract

We present an efficient implemention of a non-equilibrium Green function (NEGF) method for selfconsistent calculations of electron transport and forces in nanostructured materials. The electronic structure is described at the level of density functional theory (DFT) using the projector augmented wave method (PAW) to describe the ionic cores and an atomic orbital basis set for the valence electrons. External bias and gate voltages are treated in a self-consistent manner and the Poisson equation with appropriate boundary conditions is solved in real space. Contour integration of the Green function and parallelization over k-points and real space makes the code highly efficient and applicable to systems containing several hundreds of atoms. The method is applied to a number of different systems demonstrating the effects of bias and gate voltages, multiterminal setups, nonequilibrium forces, and spin transport.

Tuning the magnetic moments in zigzag graphene nanoribbons: Effects of metal substrates

“…To this end we calculated the forces when increasing the bias voltage. 23 The results show that the ZGNR tends to move toward the metal substrates under a negative bias but the effect is very small: The maximum force under 12 V bias voltage is found to be only 0.03 eV/Å. This effect can also be discussed from the charge transfer point of view.…”

“…Now we examine the detailed PDOS of the ZGNR after turning on the bias voltage. In the biased situation, there are two Fermi levels in the system corresponding to the two electrodes; 23 in the corresponding plots we only show the Fermi level of the left electrode (the substrate) since the ZGNR sits on the left electrode and is strongly coupled to it. For s-dominated metal substrates, the PDOS of the edge C atom under the bias voltage V b = 12 V is shown in Fig.…”

“…The properties under an external bias voltage are calculated within the nonequilibrium Green's function (NEGF) method implemented in the GPAW code, 18,23 where the nonequilibrium electron density is calculated via the Keldysh nonequilibrium Green's functions. For detailed knowledge of this method, we refer interested readers to the original literature.…”

Heterospin Junctions in Zigzag-Edged Graphene Nanoribbons

“…While the study of non-equilibrium transport, including inelastic effects, is out of the scope of this work, such a methodology can be expanded to include accurately the effect of finite bias [40,41]. In addition, it is expected that the application of a small bias will not disrupt the spin ordering, as is the case with GNRs conducting high currents [42,43]. For comparison purposes, we also plot the current flow distribution at the same energy for the corresponding homojunction.…”

Density and localized states' impact on amorphous carbon electron transport mechanisms

“…The scattering region was built with a molecule (a-C sample) and two principal layers (PL), which in our case are slabs of 3 fcc (111)Au atomic layers (a more extensive discussion on PL is found elsewhere [43][44][45][46][47] ). The Au/a-C interfaces in the scattering region were relaxed to prevent abrupt changes in the electrostatic potential.…”