Unit cell laboratory coordinate

The orientation factor provides the projection of the molecular P tensor onto the crystal or laboratory axis (note that the crystal will be oriented intentionally with respect to the applied electric field by the act of depositing electrodes on the crystal). In Eq. (8), the indices I, J, K and i, j, k refer, respectively, to the principal directions of the crystal and molecular coordinate systems. Nc is the number of equivalent positions in the unit cell. 

A complete single-crystal X-ray structure determination (Section 5.5) provides the cell dimensions, the space group, a list of positional coordinates for the atomic nuclei in the asymmetric unit, and the atomic displacement parameters (ADPs). The experiment is nowadays feasible with a modest investment of equipment money and human time, provided that a suitable crystal is available - often, the bottleneck for the productivity of an X-ray diffraction laboratory is not machine time, but the preparation of good crystal samples. The result is a high resolution picture of the molecular structure and a detailed description of the crystal packing. Through the ADPs, X-ray diffraction also provides some hints at the intra- and intermolecular dynamics. 

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