Functional groups

find_groups(structure) matches a small catalogue on the perceived bond graph and returns GroupMatch { kind, atoms }; group_counts aggregates by GroupKind. The current catalogue is hydroxyl (O with an H neighbour), carboxylate (C with two O neighbours), amine (N with one to three neighbours) and fluoride (C-F).

use xtalforge::core::find_groups;

for group in find_groups(&structure)? {
    println!("{}: {:?}", group.kind.name(), group.atoms);
}

The matcher is periodic-aware because it runs on the P1 graph. The catalogue is a fixed enum with these four patterns; the remaining patterns from Crystal-Builder core/groups.py and the framework corpus tests are not implemented. Each current pattern is tested on a small molecule.