Problem of Cohesive Energy of Nitrogen Compounds

#1

Dear mp-admins:
I got the cohesive energy by Pymatgen (get_cohesive_energy) using the Materials Project and found that most values of Nitrogen compounds are negative while those of other compounds are positive. According to the definition, the cohesive energy should be positive values. I wonder that the reference energy of N atom is wrong. Please check it. Thank you.