The computed absorption spectra of pristine and functionalized adamantane molecules are displayed in Fig 1. We found that a very rapid decrease of the absorption gap when replacing H with Li or Na atoms in adamantane molecules. It is observed that Li-added continuously decrease of the absorption gap but Na adding case when 3-Na-added absorption gap a little increase which are agreement with electronic gap results from B3LYP/aug-cc-pVDZ functional in the table 1. In fact the optical gap is not the orbital energy difference between HOMO-LUMO gaps but its energy difference the S0 and S1 states. So, the optical gap of all molecules is obtained from absorption spectra by TD-DFT calculations