The negative behavior implies that

The negative behavior implies that adding one electron to form an anionic system leads to the higher in energy than the ground state energy of the neutral system. In contrast, the positive behavior indicates that the ground state energy of the neutral systems is lower than that of the anionic systems. An appearance of the negative EA of the pristine adamantane indicates that the conduction band minimum is above the vacuum level. Consequently, it favored to receive electrons. However, all structures of the modified adamantane give the positive EA. This suggested that they favored to donate electrons. According to the IP energy, it was dramatically decrease when one Li or Na atom was substituted in the adamantane structure and adding more Li or Na atoms results small change in the EA.