An effective search for new organic crystals for prospective use in nonlinear optical (NLO) applications requires quantitative and fast experimental determination of their NLO properties at a molecular level. However, the growth of sufficiently large single crystals, which are needed for structural analysis and refinement by X-ray methods, is a time-consuming and sometimes impossible task. Single crystals of a considerably smaller size may be effectively used for complete structural analysis by electron diffraction combined with simulation methods. When the crystal structure of a given compound is known, its NLO properties may be estimated using quantum-chemical methods for calculation of the molecular nonlinearity tensor and the relationships between its components and the macroscopic coefficients of the crystalline nonlinearity tensor. In the present work, the semiempirical PM-3 method was employed for this aim.

The structure of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) has been reinvestigated by a combination of electron diffraction, high-resolution imaging, simulations of electron diffraction patterns and images, and packing energy calculations. A new model is proposed that is capable of explaining the large second harmonic generation effect observed in TATB crystalline powder.

No abstract