GAMGI Tutorials: NaCl crystalline structure

# NaCl crystalline structure

- Page 1

The NaCl rocksalt structure is widely observed in ionic crystals, with equal number of cations and anions, when the cation is significantly smaller than the anion: NaCl, KCl, LiF, MgO, CaO, SrO, NiO, CoO, MnO and PbO.

To build this structure, first we create the cell with the observed lattice parameters, then the Na, Cl atoms used as models, with the observed ionic radius, and then link the cell with the atoms.

1. Press Cell->Create and set System to c, Lattice to F (Face-Centered Cubic) and a to 5.660 (so the ions will be in contact along <100> directions). Press Ok to create the cell.
2. Select Atom->Create and set Style to Solid, Size to 1.0 and Variancy to 1.0. Set Element to Na, Radius to 1.020 (ionic radius for Na+) and press the mouse over the graphic area. A Na atom is created where the mouse was pressed.
3. Set Element to Cl, Radius to 1.810 (ionic radius for Cl-) and press the mouse over the graphic area. A Cl atom is created where the mouse was pressed.
4. Press Cell->Link and select the Crystal link method. Press the mouse over the cell, and then over the Na atom, to identify the objects to link. Set the x, y, z coordinates (Position page) to 0.5, 0.0, 0.0 and press Ok. 13 Na atoms are now visible, 12 in the edges and 1 in the center, corresponding to a total of 4 Na atoms inside the cell.
5. Repeat the link procedure above, but this time pressing the mouse over the Cl atom, and setting the x, y, z coordinates to 0.0, 0.0, 0.0. 14 Cl atoms are now visible, 8 in the vertices and 6 in the face, corresponding to a total of 4 Cl atoms inside the cell.
6. Select Light->Create and press Ok, to add a light and give atoms a three dimensional look.
7. Remove the Na,Cl atoms used as models during the building process, pressing Atom->Remove and clicking the mouse over the two atoms.
8. Rotate,move,scale the NaCl cell with the mouse. Press Atom->Measure to determine lengths and angles between atoms.
9. Repeat the whole procedure, this time setting the cell type in Cell->Create (Type page) to: 1) Primitive; and 2) Wigner-Seitz.

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