Two PBFs 𝑝 1 and 𝑝 2 are said to be 'stacked' when they satisfy all of the following criteria: 1. The smallest angle between their plane normals (𝑛 1 , 𝑛 2 ) is less than 25 degrees, 2. The distance between the two plane centroids is less than 8.0 Å, 3. The smallest angle between the vector from centroid 𝑐 1 to centroid 𝑐 2 (𝑐 12 ) and normal 𝑛 1 is less than 30 degrees. 4. The closest distance between the two planes (i.e. projection of 𝑐 12 in 𝑛 1 ) is less than 6.0 Å. 5. The overlap (as specified above) between the two planes is more than 30%.