Periodic bond chain models, crystal

In 1955, Hartman and Perdok (18) refined the BFDH model by relating the crystal morphology to its internal structure on an energy basis. They identified that chains of strong intermolecular bonds known as periodic bond chains (PBC) govern the crystal morphology. According to the number of PBC inside a slice of thickness, they classified the crystal faces as (i) F-faces (flat), two or more PBC, (ii) S-faces (stepped), one PBC, or (iii) K-faces (kinked), zero PBC. 

Hartman and Bennema (1980) proposed the attachment energy model, which relates the energies of the bonds between the crystal-building units to its external shape. Two important concepts were developed as part of this model—the periodic bond chains (PBCs) that define periodically repeated chains of strong intermolecular interactions and the attachment energy (fi tt)- Based on the number of PBCs that are parallel to a face, crystal faces can be classified as flat (F) face with 2 PBCs, step (S) face with 1 PBC, or kink (K) face with 0 PBCs. The morphological importance of the faces follows... 

---