title: Why is the crystal shape of TATB is so similar to its molecular shape? Understanding by only its root molecule.
abstract: We present an understanding of the quasi-regular or regular hexagonal enlargement of 1,3,5-triamino-2,4,6 (TATB) from its root molecule to its bulk crystal, by only its root molecule. That is, the mechanism of regular hexagonal TATB molecules stacking to a quasi-regular or regular hexagonal TATB crystal was discussed using a combined method of a density functional theory BLYP and Dreiding forcefield, and a series of static scanning calculations. As a result, we found that there are two styles of forming the most energetically favored TATB dimers: a hydrogen bonding along the molecular plane and an offset π-stacking vertical to the plane, just leading to the outspread and the thickening of the regular hexagon during the crystal growth, respectively. At the same time, it was found that the rotation of one TATB layer in any parallel stacked double-layer should overcome a very high energy barrier. It suggests that the TATB molecules or layers are arranged on the crystal face always along the special orientation of a regular hexagon and other orientations are strongly thermodynamically forbidden, resulting in a hexagonal crystal bulk.
authors.affiliation: Laboratory of Material Chemistry, Institute of Chemical Materials, China Academy of Engineering Physics (CAEP), Mianyang, Sichuan, People's Republic of China. zcy19710915@yahoo.com.cn
authors.forename: Chaoyang
authors.initials: C
authors.lastname: Zhang
authors.forename: Bin
authors.initials: B
authors.lastname: Kang
authors.forename: Xia
authors.initials: X
authors.lastname: Cao
authors.forename: Bin
authors.initials: B
authors.lastname: Xiang
mesh_terms: D003460:Crystallization; D018360:Crystallography, X-Ray; D019281:Dimerization; D006860:Hydrogen Bonding; D008958:Models, Molecular; D015394:Molecular Structure; D011789:Quantum Theory; D013816:Thermodynamics; D014301:Trinitrobenzenes / Q000737:chemistry*
chemical_list: D014301:Trinitrobenzenes; C512607:1,3,5-triamino-2,4,6-trinitrobenzene