Unraveling the Influence of Molecular Vibrations on Electron Transport in Single-Molecule Junctions via Ab Initio Quantum Chemical Modeling

A computational methodology, founded on chemical concepts, is presented for interpreting the role of nuclear motion in the electron transport through Single-Molecule Junctions (SMJ) using many-electron ab initio quantum chemical calculations. Within this approach the electron attached states, modeling the system formed upon the arrival of an excess electron from the bulk, are computed at the SOS-ADC(2) level along the individual normal modes of the encapsulated molecules. The inspection of the changes in the partial charge distribution of the many-electron states allows the quantification of the electron transport and the estimation of transmission probabilities. This analysis improves the understanding of the relationship between internal motions and electron transport. Two SMJ model systems are studied for validation purposes, constructed from a conductor (BDA, benzene-1,4-diamine) and an insulator molecule (DABCO, 1,4-diazabicyclo[2.2.2]octane). The trends of the resulting transmission probabilities are in agreement with the experimental results, demonstrating the capability of the approach to distinguish between conductor and insulator type systems, thereby offering a straightforward and cost-effective tool for such classifications via quantum chemical calculations.