# Bond-angle analysis

This modifier identifies the local environment of particles using the Ackland-Jones bond-angle method [Ackland and Jones, Phys. Rev. B 73, 054104] and assigns a structure type (FCC, BCC, HCP etc.) to each particle.

The modifier stores the results in the `Structure Type` particle property. This allows you to subsequently select particles of a certain structural type, e.g. by using the Select Particle Type modifier. The structural type of each particle is encoded as an integer value:

- 0 = Other, unknown coordination structure

- 1 = FCC, face-centered cubic

- 2 = HCP, hexagonal close-packed

- 3 = BCC, body-centered cubic

- 4 = ICO, icosahedral coordination

An alternative structure identification method is provided by the Common Neighbor Analysis modifier. To identify diamond lattice structures, the Identify Diamond Structure analysis modifier can be used.

Note that this modifier requires access to the complete set of input particles to perform the analysis. It should therefore be placed at the beginning of the processing pipeline, preceding any modifiers that delete particles.

The Use only selected particles option restricts the analysis to the currently selected particles. If this option is checked, unselected particles will be ignored (as if they did not exist) and will be assigned the structure type "Other". This option can be useful if you want to identify defects in a crystal with a structure not supported by this analysis algorithm, but which has a sublattice that can be identified by the bond-angle method (and you do not want to delete particles belonging to the other sublattice(s) for some reason).