What is the Difference Between Unit Cell and Primitive Cell?
🆚 Go to Comparative Table 🆚The difference between a unit cell and a primitive cell lies in the number of lattice points they contain and their geometry. Here are the key differences:
- Unit Cell: A unit cell is the smallest repetitive unit of a crystal system that represents the repeating pattern of the lattice structure. It is a three-dimensional structure and can be defined as the smallest group of atoms that has the overall symmetry of a crystal, from which the entire lattice can be built up by repetition in three dimensions.
- Primitive Cell: A primitive cell is a type of unit cell that contains exactly one lattice point. It is the smallest possible unit cell of a lattice. In a primitive cell, lattice points are located at each of its eight vertices. Primitive cells can be either two-dimensional or three-dimensional structures.
In summary, a unit cell is a more general concept representing the smallest repetitive unit of a crystal system, while a primitive cell is a specific type of unit cell that contains only one lattice point.
Comparative Table: Unit Cell vs Primitive Cell
The main difference between a unit cell and a primitive cell is that a unit cell is the smallest group of atoms that has the overall symmetry of a crystal, while a primitive cell is the smallest possible unit cell of a lattice. Here is a comparison table highlighting the differences between unit cells and primitive cells:
Feature | Unit Cell | Primitive Cell |
---|---|---|
Geometry | Parallelepiped (3D) or Parallelogram (2D) | Parallelogram (2D) or Parallelepiped (3D) |
Lattice Points | Several lattice points | One lattice point in each of its eight vertices |
Dimension | Three-dimensional structure | Two or three-dimensional structure |
Symmetry | Reflects the symmetry of the crystal | May not reflect the symmetry of the crystal |
A unit cell is a repeating part of the crystal structure, and its geometry can be parallelepiped or parallelogram depending on the space dimension (3D or 2D). On the other hand, a primitive cell is the smallest minimum volume cell corresponding to a single lattice point of a structure, and its geometry can also be parallelogram or parallelepiped depending on the space dimension (2D or 3D). The primitive cell is often used as a simpler representation of the unit cell in crystallographic investigations and computational materials science.
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