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

TL;DR

This paper introduces advanced methods and algorithms in the next-generation DFT-NEGF code 'transiesta' for scalable, multi-electrode quantum transport simulations, enhancing performance, flexibility, and applicability to large systems.

Contribution

The paper presents novel algorithms and features in the DFT-NEGF code 'transiesta' for improved scalability, multi-electrode handling, and advanced post-processing capabilities, enabling large-scale quantum transport simulations.

Findings

Demonstrated improved performance and scalability on large systems.

Enabled multi-electrode and complex device simulations.

Validated new methods with benchmark tests.

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 ($N_e\ge1$) with individual chemical potentials and electronic temperatures. We describe its novel methods for electrostatic gating, contour opti- mizations, and assertion of charge conservation, as well as the newly implemented algorithms for optimized and scalable matrix inversion, performance-critical pivoting, and hybrid parallellization. Additionally, a generic NEGF post-processing code (tbtrans/phtrans) for electron and phonon transport is presented with several novelties such as Hamiltonian interpolations, $N_e\ge1$ 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 $10^6$ atoms on workstation computers. The new features of both codes are demonstrated and bench-marked for relevant test systems.