Lattice Parameters¶
Open the Lattice Parameters dialog with Crystallography → Set Lattice Parameters.
Lattice parameters define the crystal's unit cell geometry. They are required to:
- Use Miller index (h k l) input for planes
- Use fractional [u v w] input for directions
- Display crystallographic a/b/c axes instead of Cartesian X/Y/Z
Parameters¶
| Parameter | Symbol | Unit | Description |
|---|---|---|---|
| a | a | Å | Unit cell length along a |
| b | b | Å | Unit cell length along b |
| c | c | Å | Unit cell length along c |
| Alpha | α | ° | Angle between b and c |
| Beta | β | ° | Angle between a and c |
| Gamma | γ | ° | Angle between a and b |
For a cubic crystal: a = b = c, α = β = γ = 90°.
Input Methods¶
Manual Entry¶
Enter each parameter directly into the number fields. Click OK or Apply to save.
Validation: Cell lengths must be positive; angles must be between 0° and 180°.
From CIF File¶
Click Load CIF and select a .cif (Crystallographic Information File). The lattice parameters are extracted automatically from the _cell_length_* and _cell_angle_* fields.
From CrystoGen Structure File¶
Click Load Structure File and select a CrystoGen output structure file. The lattice parameters are extracted from the file header.
Effect on the Application¶
Once set, lattice parameters affect:
- Planes dialog: Miller (h k l) mode becomes available
- Directions dialog: Fractional [u v w] mode becomes available
- Axes: The a/b/c fractional axes are computed and can be displayed (
Shift+A) - Coordinate display: Miller indices are shown alongside Cartesian normals
Auto-Loading¶
If a structure file is present in the loaded data folder, CGAspects automatically reads the lattice parameters on import. You can still override them manually in this dialog.
Coordinate Transformations¶
CGAspects converts between coordinate systems using standard crystallographic transformations:
- Miller indices (h k l) → Cartesian normal: via the reciprocal lattice metric tensor
- Fractional indices [u v w] → Cartesian vector: via the direct lattice metric tensor
These conversions use the lattice parameters you provide.