The calculation of the electronic and transport properties of metal/molecule junctions is of paramount importance in many fields of molecular nanoscience. DFT struggles to accurately predict the energy level alignment between the frontier molecular orbitals and the Fermi level of the metal. Several approaches have been proposed to calculate the energy level alignment of metal/molecule interfaces beyond DFT, among them the DFT+Σ method [1] stands out as it reduces computational cost while maintaining good accuracy. Here, we develop a new method to correct the DFT-based energy level alignment of molecular junctions. We start by projecting the orbitals of the molecular subspace onto the full junction space. The projection coefficients are used to average parameters from DFT+Σ framework (gas phase and polarization). At variance with previous approaches we introduce the correction in the total junction Hamiltonian, i.e., operator is defined in junction space. Using this methodology we are able to correct the complete electronic structure. We have implemented this method in the DFT SIESTA code [2] because it describes electrons in a localized basis set, allowing for an unambiguous clustering of the system. We will show results for typical metal/molecule/metal junctions.
[1] S. Quek, et al. Nano Lett. 7, 3477 (2007).
[2] J. M. Soler, et al. J. Phys. Cond. Matt. 14, 2745 (2002)
International mobility MSCA-IF II IOP, CZ02.2.69/0.0/0.0/18_070/0010126.