To computationally predict the Xe/Kr selectivity of a COF, we are armed with two different molecular simulation techniques. Each molecular simulation employs Lennard-Jones interatomic potentials (parameters from Universal Force Field 88 ) to describe the potential energy of a configuration of a rigid COF hosting Xe and/or Kr adsorbate(s). Given a COF, our choice of which simulation to perform to predict its Xe/Kr selectivity involves a trade-off between fidelity and computational runtime.