Comparing with the band gap of the pristine adamantane obtained from the experiment of 6.03 eV [14], it is clearly seen that the SVWN/aug-cc-pVDZ level of the theory is the best choice because it gives the smallest relative energy difference of 4.51 %. The electron affinity (EA) and ionization potential (IP) energies of all structures were given in Table 2. The electron affinity is defined as the amount of energy of released when an electron is added to neutral system and the ionization energy is defined as the amount of energy required to remove electron from the molecules. Thus, these energies can be calculated as follows