Spatial probability density of the adsorbates. During a GCMC simulation, we estimate the spatial probability density of adsorbates inside the MOF as follows. First, at the beginning of the simulation, we partition the volume in the simulation box into a regular grid (in fractional coordinate space) of volume elements (voxels) and initialize adsorbate counts in each voxel as zero. We chose the number of voxels in each direction so that the side length is ă 0.20 Å, giving a ˆ ˆ grid of voxels.