A grand canonical (constant µVT) Monte Carlo simulation method was implemented in order to determine the equilibrium gas adsorption at different pressures and temperatures. The method, based on Frenkel and Smit , was written in Python. The host molecules were held fixed, and only the guest molecules were subject to Monte Carlo moves. Insertions, deletions and translations were equally likely to be attempted. Translations and insertions were always performed after the molecule had been randomly rotated. Insertions and translations were attempted at randomly chosen positions independent of the molecule's previous position. Pseudo-random numbers were used, and uniformly distributed rotation matrices were generated with Arvo's fast method . Simulations were performed on supercells created by elongating the single shortest lattice vector until the supercell contained 16 molecules of TTBI or 18 molecules of the other compounds. The program DMACRYS and the multipolebased force field described above were used to calculate the energy of the Monte Carlo configurations. However, for computational speed and convenience, it is necessary to identify and reject simulation frames containing atom clashes, i.e.