The procedure to calculate the GRID is as follows: 1) compute all pairwise distances up to an arbitrary cutoff (here 10 Å) starting from each symmetry-unique atom (j) within the unit cell, taking periodic boundary conditions into account; 2) rank the distances dj = {d1j, … , dij, …} in ascending order and then assign the ith-ranked value to the ith GRID 'group'; 3) to achieve a fixed-length descriptor, discretize the dij values of the ith group into a binned histogram, after smoothing them using a squared exponential kernel to avoid discontinuous jumps between bins caused by numerical or experimental error;