14 Bravais-lattice types are known, commonly distingusihed as primitive (P), body-centered (I), face-centered (S representing A,B and C), rhombohedral (R) and all-face-centered (F).
CALM uses the nomenclature according to [1,2] listed in the following table.
The numbers at the top of each column indicate the amount of lattice points per unit cell.
This is quite useful since the described unit cell volume in CALM has to scale with this number if the description of the lattice is uniform and consideres all defined bands.
Different Bravais lattice types used in CALM. The rhombohedral lattice is only considered as primitive description.
CALM will always refer to a single (aP) but commonly to more solutions.
The number of solutions depends on the size of the maximum deviations adjustable in degrees for symmetry-specific angles and in % for symmetry-specific lattice-parameter ratios.
If such conditions for angles and ratios are irrelevant for the given lattice solution, the shown maximum deviations are meaningless.
Please note: The centering S for monoclinic and orthorhombic depends on the lengths of a, b and c, since for orthorhombic solutions in CALM is valid: a ≤ b ≤ c.
This means, if a centering is perpendicular to b*, S becomes B. If the centering is Ʇa*, S = A.
Maximum deviations
Only for computed trace positions and simulated patterns CALM will give unique Bravais lattice type descriptions. In case of experimental patterns and manually defined four initial traces maximum deviations for the ratios and the angles between basis vector lengths are defined. They enable to display all possible supergroups, i.e., the actual solution is always triclinic (aP) but can have the potential of a higher symmetry, see the following table.
Table 3.4.1.3. The Bravais-lattice type of the three-dimensional lattice at the upper end of a line is a limiting case of the type at the lower end.
International Tables for Crystallography, Vol.A (2016) , p. 717
The scheme means: A lattice decribed as oC might become also hP, tP or cP if the maximum deviations are increased further, but change to either mP, mI or even aP if the maximum deviations will be reduced.
Commonly, as most probable lattice description the highest symmetric solution is used.
[1] de Wolff, P. M. et al. Acta Cryst. A41 (1985) 278-280
[2] Hahn, T,: International Tables for Crystallography, Vol.A (2005), 5th ed., Springer,Table 2.1.2.1, p.15