Non-crystallographic Symmetry Interactions

If strict non-crystallographic symmetry is imposed, the crystal symmetry interactions cannot be computed because of nonequivalent environments (see Chapter 18). Instead, only the interaction between non-crystallographically related molecules is computed using the $f_{VDW}$ and $f_{ELEC}$ functional forms, i.e.,

$$E_{PVDW} = \sum_{S{\in}NCS} \sum_{i<j} f_{VDW} (r_{i} - Sr_{j})$$ (4.23)

$$E_{PELE} = \sum_{S{\in}NCS} \sum_{i<j} f_{ELEC} (r_{i} - Sr_{j})$$ (4.24)

The atom/group search and the update of the interaction list are carried out analogously to the intramolecular case. (Refer to Chapter 18 for the definition of non-crystallographic symmetry operators.)