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

The nonequilibrium 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 junction structures and understanding the functionality of molecular devices. In this study, we developed a series of computational methods capable of effectively handling the molecular Hamiltonian, electrode electronic structures, and their interfacial coupling at different theoretical levels. As three-tiered hierarchical levels, they enable efficient charge transport computations ranging from individual molecules to complete junction systems, achieving an optimal balance between computational cost and accuracy. Moreover, integrated into a Question-Driven Hierarchical Computation (QDHC) framework, we show this three-tiered framework is able to address specific research objectives by isolating and analyzing the dominant factors governing charge transport, thus significantly enhancing the efficiency of analyzing charge transport mechanisms, as validated through a series of benchmark studies on diverse molecular junction systems.