Investigation on the chemical active sites of copper nanoclusters as nanocatalyst for the adsorption of acetylene: calibration of DFT method and basis set

A complete minimum-energy structural search was carried out for the adsorption of C2H2 molecule on the copper nanoclusters with special attention paid to the most favored adsorption sites. At first, DFT functionals were calibrated with different basis sets including LANL2DZ, 6-31+G*, 6-311+G* and cc-pVTZ in order to calculate the geometry and electronic properties of pure and interacting copper nanoclusters [Cu (n) and Cu (n) C2H2 (n a parts per thousand currency sign 9)]. The accuracy of the DFT calculations was assessed by comparing them with the experimental values as well as MP2 and CCSD(T). The results showed that TPSSTPSS functional of DFT performed better than all other functionals. The accepted basis sets for the pure and interacting copper nanoclusters were LANL2DZ and "LANL2DZ+aug-cc-pVTZ," respectively. A relationship between the size of the copper nanoclusters and the chemical reactivity was also established. For this purpose, the adiabatic ionization, adiabatic electron affinity, chemical hardness, electronic chemical potential and electrophilicity were evaluated. According to the obtained results, the C2H2 adsorption on the copper nanoclusters was selective in the terminal coordination. Furthermore, the favored adsorption sites were dominated by the local orientation of the relevant frontier orbitals as well as the distribution of the overall electrostatic potential surfaces of the copper nanoclusters.