A Three-Tiered Hierarchical Computational Framework Bridging Molecular Systems and Junction-Level Charge Transport

Abstract

The Non-Equilibrium Green's Function (NEGF) method combined with ab initio calculations has been widely used to study charge transport in molecular junctions. However, the significant computational demands of high-resolution calculations for all device components pose challenges in simulating junctions with complex molecular structures and understanding the functionality of molecular devices. In this study, we developed a series of approximation methods capable of effectively handling the molecular Hamiltonian, electrode self-energy, and their interfacial coupling at different levels of approximation. These methods, as three-tiered hierarchical levels, enable efficient charge transport computations ranging from individual molecules to complete junction systems, achieving an optimal balance between computational cost and accuracy, and are able to addresses specific research objectives by isolating and analyzing the dominant factors governing charge transport. Integrated into a Question-Driven Hierarchical Computation (QDHC) framework, we show this three-tiered framework significantly enhances the efficiency of analyzing charge transport mechanisms, as validated through a series of benchmark studies on diverse molecular junction systems, demonstrating its capability to accurately and efficiently elucidate charge transport mechanisms in complex molecular devices.