Two residues that are difficult to classify in our data set. Two residues that are difficult to classify in our data set. In (a), ARG-17 of BPTI (in yellow) in bovine chymotrypsin (in green)-BPTI complex [PDB:1CBW] is shown. This residue is a non hot spot residue (∆∆G=0.5 kcal/mol) with an extremely low SASA (8.0 Å2). In (b), TYR-29 of barstar (in yellow) in barnase (in green)-barstar complex [PDB:1BRS] is shown. This residue is a hot spot residue (∆∆G=3.4 kcal/mol), but it has a large SASA (64.12 Å2). These two residues have been correctly classified by our method. The dashed lines in the figures are Type-II atomic contacts (candidates of hydrogen bonds).