New chemical approaches for conversion of N2 to NH3, as an alternative to the energy- and CO2-intensive Haber-Bosch process, are of high interest for improved fertilizer production and the potential of NH3 as a zero-carbon fuel. Catalytic N2 fixation, however, is an extremely difficult reaction with few successes. Previous attempts show low turnover rates, insufficient selectivity or too negative potentials required. A breakthrough in molecular N2 fixation was recently described (J. C. Peters and co. Nature, 2022). By combining coupled proton-electron transfer mediator, CPET, with simple Fe/Mo/W complexes in solution, selective catalysis was demonstrated (-1.2 V vs. Fc0/+). This proof-of-principle experiment implicates CPET mediation as a general N2 fixation strategy when combined with N2-binding metal complexes. However, design principles for improving catalytic N2 fixation activity under CPET conditions are not known. We propose here a multiscale simulation strategy to uncover these catalyst design principles and aid synthetic efforts. Our previous expertise in studying biological N2 fixation, multiscale modelling of redox processes and high-level calculations of redox mediators will be of benefit in this project.