Energy and the Molecular Coordination Sphere

Each molecule in the model crystal cluster is identified by a symmetry operator, O(y ), connecting it to the reference one, by a distance, R(J) (usually between centers of mass), and by E J), as described above. For comparisons, E(J) is usually expressed as a percent of the total (PPE) the assembly of molecules with (y) 0.02 (PE) is taken as the molecular coordination sphere (see 12.4.3). 

The relative importance of each operator in the crystal structure can be determined by summing all the E JYs for molecules generated by that operator, yielding the overall percentage of the packing energy due to it. 

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