We predict the equilibrium, pure-component Xe, Kr, and Ar adsorption isotherms using grandcanonical Monte Carlo (GCMC) simulations . GCMC simulations are Markov Chain Monte Carlo (MC) simulations of the grand-canonical (GC) statistical mechanical ensemble. In the GC ensemble, a fixed volume of the (rigid) MOF is immersed in a bath of pure gas at a fixed chemical potential and temperature. Our simulation volume consists of the Ni(PyC-X) 2 unit cell replicated sufficiently such that a sphere of radius r cutoff " 14 Å fits inside of it (e.g. ˆ ˆ for functionalized MOFs). In the GCMC simulation, we propose, as transitions between microstates, particle insertions, deletions, translations, and re-insertions with probabilities: . , . , . , and . , respectively. We compute the change in the potential energy of the system upon each proposed microstate transition using the force field described in Sec. . . . The acceptance criteria for the microstate transitions are dictated by the Metropolis-Hastings acceptance rules. For each GCMC simulation, we use burn cycles followed by production cycles over which samples of the number of adsorbates, potential energy, and adsorbate positions are collected. A cycle is defined as maxp20, nq microstate transition proposals, where n is the number of adsorbates in the system at the beginning of the cycle.