Pharmacophoric feature classes used by FCFP, in RDKit bit order
Source:R/fcfp4_native.R
MORIE_FCFP_FEATURE_CLASSES.RdThe order in which morie_fcfp4 packs the six
functional-class flags of each atom into its round-0 identifier:
donor, acceptor, aromatic, halogen, basic, acidic.