From DFT to compact non-local model: Accurate and efficient Hückel-based simulation of molecular electronic devices

The implementation of simple models similar to those used in semiconductor chip design can accelerate progress in molecular electronics. To elaborate a model of such type, we perform ab initio calculations of electron transport through polyene and polyphenylene molecular conductors under both zero and finite bias conditions, using various anchor groups (thiomethyl, pyridine, and benzo[b]thiophene) attached in both symmetric and asymmetric configurations. Based on the resulting transmission spectra, we propose a phenomenological Hückel Hamiltonian fitting model that is both accurate and relatively simple. This model remains consistent, as parameters extracted from symmetric anchor configurations at zero bias can be applied to asymmetric cases under both zero and finite bias conditions. We find that parameters related to the molecule-electrode interface (tunneling coupling and energy shift) are predominantly anchor-specific and show only weak dependence on the molecular conductor's internal structure. In contrast, parameters describing the redistribution of charges along the molecule are of a non-local nature and demonstrate a strong dependence on intramolecular conduction. The proposed model, as well as the obtained numerical values of the parameters for common anchor groups, enables straightforward yet realistic studies of molecular electronic devices at the Hückel Hamiltonian level.