GAMGI Interfaces: Cell Link

# Cell Link

- Object
- Position
- Occupancy
- Packing

Define here the position of the linked objects.

### Vectors

Object coordinates can be given in terms of the vectors defining: 1) the Conventional cell; 2) the Primitive cell, 3) the absolute Local referential of the current Layer. Users can enter coordinates using any of the three referentials, independently of the actual Cell volume.

In order to apply space group information, coordinates are first converted internally to conventional vectors. After generating all the Wyckoff positions, these coordinates are converted to primitive vectors. These are applied when the cell volume is Primitive, Wigner, Rhombus or Sphere.

### Wyckoff

When the crystallographic space group is known, GAMGI lists all its Wyckoff sites, showing for each one: 1) the number of replicas that will be generated for each node (i.e. the order of the point group of symmetry of that site); 2) the label of the Wyckoff site, starting from "a" to "z", as in the International Tables for Crystallography (and then "A", for space group 47); 3) the oriented point symmetry of the site, as in the International Tables for Crystallography.

When space group information is unknown, the linked object is handled just as part of a base or motif, so only one position is generated for each node (the space group and site point symmetry are assumed to be 1) and the menu has just one menu item: "1 Basis 1".

### x, y, z

For the general Wyckoff site, with point symmetry 1, all x,y,z coordinates are needed and the corresponding entries are all active. For sites with higher symmetry, unnecessary coordinates are automatically disabled.

Before generating the required Wyckoff positions, GAMGI always tries to find equivalent positions. When redundant positions are found, they are discarded, and GAMGI tries to find a Wyckoff site with higher symmetry that generates exactly the same set of non-redundant positions. A warning dialog is then produced with the obtained information, and the link operation proceds using just the non-redundant positions.
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