When binding to the Mpro cavity, a thioimidate adduct sub-structure is formed when the nitrile N40 interacts with the sulfur of Cysteine 145. Although these and neighboring atoms are involved in the reaction, other atoms have an effect in anchoring the ligand to the protein in order to initiate the reaction. GOLD is used in covalently attaching the (H deleted) CYS 145 to the (H ignored) N40 and the total score distribution is shown in Figure . This translates to a difference of 30/4.184=7.17 kcal. Given the heuristic of 6.5 score to 1 kcal, 47 is covalent score difference from 7.17 kcal. The highest non-covalent interaction score of ~70 is now in the covalently bonded distribution ~116, for a difference of 46. Surprisingly, this matches with the bond energy change of ∆score 47 and the approximate heuristic of 6.5 per 1 kcal. (Details of covalent interaction is included in the GOLD output when the per_atom_score flag is 1.)