In this work, the adsorption of cyanogen (NCCN) molecule on the external surface of pristine and Cu-decorated Si12C12 (Cu@Si12C12) nanocage has been reported using density functional theory (DFT) calculations at the WB97XD/6-31 + G(d) level. The weak physisorption can be seen for the adsorption of the NCCN molecule onto the pristine nanocage. Thus, the structural and electronic properties of the pristine Si12C12 do not change dramatically by the adsorption process. As a result, Si12C12 nanocage cannot be a proper sensor for detecting and sensing NCCN molecule. In order to improve the properties of the nanosensor, Cu decorating process was investigated. Results obtained show that on the effectiveness of this process, the electrical properties of Si12C12 are considerably changed. In addition to, we investigated the adsorption of the NCCN molecule on to the external surface of Cu-decorated Si12C12 (Cu@Si12C12). According to the results of the calculations, this process is chemisorptions with the adsorption energy (Eads) in about −102.84 kJ · mol−1 and also in this process; the value of energy gap (Eg) is significantly decreased. Therefore Cu@Si12C12 is a suitable adsorbent and it is expected that can potentially to be used as nanosensors for detecting the presence of toxic NCCN molecule
