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Lattice
Points
· For
each of the different unit cell classes of the Bravais
lattice, all cells within a class ( P, C, F, I) obey the same constraints
of sides and angles.
·
All cells within the same class have the same symmetry.
·
Lattice points are fractionally assigned to a unit cell:
"Corner"
points are assigned 1/8 to a cell
"Face"
points are assigned 1/2 to a cell
"Body"
points are assigned 1 to a cell
·The
total number of lattice points per cell is computed by adding together
the fractions of each point in that cell.
| Cell type |
Points per cell |
| Primitive
cell (P) |
8
x 1/8 |
=
1 |
| Body
Centered cell (I) |
(8
x 1/8) + (1 x 1) |
=
2 |
| Base
Centered cell (C) |
(8
x 1/8) + (2 x 1/2) |
=
2 |
| Face
Centered cell (F) |
(8
x 1/8) + (6 x 1/2) |
=
4 |
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