Quantum Electronic and Thermoelectric Transport Properties through an Au-BDPA-Au Molecular Junction: A DFT+NRG Study

Organic thermoelectrics have been considered as a promising candidate for flexible, large-area, and low-cost energy generation or heating-cooling devices. Thanks to their intrinsic spin states, magnetic molecules are very attractive for designing high-performance thermoelectric devices. However, due to the strong interactions between π-electrons, a universal theoretical framework for the thermoelectric transport properties of organic magnetic molecules is still lacking. In this paper, we focus on a Au-α, γ-bisdiphenylene-β-phenylallyl (BDPA)-Au molecular junction. By combining the first-principles calculation with the nonperturbative numerical renormalization group method, and employing the single-orbital Anderson model, we systematically analyze its quantum electronic and thermoelectric transport properties. We find that the BDPA maintains its open-shell state and even connects with the Au electrodes, with the Kondo resonance originating from the unpaired electron on the singly unoccupied molecular orbital of the π-type. Near the particle-hole symmetric point, the electrical and thermal conductivities exhibit resonant peaks. Moreover, by adjusting the energy levels, the Seebeck coefficient can be altered, thereby achieving a high thermoelectric figure of merit. These findings provide useful insights for investigating the thermoelectric properties of metal-free radical molecules, and our suggested "ab initio + model calculation" theoretical framework may bring a promising methodology for exploring the complex π-electron magnetism dominant thermoelectric transport in real magnetic nanosystems.