A density functional theory calculation for determining the I-V characteristics (admittances of molecules) in molecular-based junctions is presented here. The efficacy of this method is shown by calculations of I(V) characteristics on an S-(p-C6H4)-S between proximal Au atoms and comparing the data to the results obtained experimentally. Over the range studied experimentally, the calculations here corroborate well with the I(V) characteristics found in molecular junction experiments.