Function perceive 

pub fn perceive(top: &mut Topology) -> Perception

Perceive rings + aromaticity for a topology, annotating it in place: sets BondOrder::Aromatic on the bonds of every aromatic ring, and the in-ring / aromatic flag bits on the atoms. Sums the partial charges up front. Returns the Perception (rings + net charge).

Destructive of Kekulé structure (an aromatic ring’s bonds all become Aromatic); idempotent. See also System::perceive.