Improvements on non-equilibrium and transport Green function techniques: The next-generation transiesta

TLDR

The authors introduce novel density‑functional‑theory based methods into the NEGF code TRANSIESTA. They extend TRANSIESTA to support multiple electrodes with independent potentials and temperatures, implement electrostatic gating, contour optimization, charge‑conservation checks, efficient matrix inversion and hybrid parallelization, and provide a generic post‑processing toolkit (TBTRANS/PHTRANS) with Hamiltonian interpolation, multi‑electrode support, bond‑current analysis, user‑defined tight‑binding interfaces, transmission projection, and scalable inversion for systems exceeding 10⁶ atoms. The enhanced TRANSIESTA and TBTRANS/PHTRANS features are validated and benchmarked on representative test systems.

Abstract

We present novel methods implemented within the non-equilibrium Green function code (NEGF) TRANSIESTA based on density functional theory (DFT). Our flexible, next-generation DFT–NEGF code handles devices with one or multiple electrodes (Ne≥1) with individual chemical potentials and electronic temperatures. We describe its novel methods for electrostatic gating, contour optimizations, and assertion of charge conservation, as well as the newly implemented algorithms for optimized and scalable matrix inversion, performance-critical pivoting, and hybrid parallelization. Additionally, a generic NEGF “post-processing” code (TBTRANS/PHTRANS) for electron and phonon transport is presented with several novelties such as Hamiltonian interpolations, Ne≥1 electrode capability, bond-currents, generalized interface for user-defined tight-binding transport, transmission projection using eigenstates of a projected Hamiltonian, and fast inversion algorithms for large-scale simulations easily exceeding 106 atoms on workstation computers. The new features of both codes are demonstrated and bench-marked for relevant test systems.