Adsorption of CO on pure and mixed clusters of tin and germanium up to five atoms: A theoretical study

The adsorptions of the CO molecule on the neutral mixed clusters of Sn and Ge up to five atoms are investigated theoretically. Electronic structures of the cluster-CO complexes are obtained by global optimization of the energy surface using Monte Carlo simulation coupled with simulated annealing followed by pseudopotential plane wave density functional theory calculations. An aug-cc-pVTZ basis set for C and O and aug-cc-pVTZ-pp for Sn and Ge atoms are employed. The CO adsorption energies and Gibbs free energy are calculated to establish the kinetic and thermodynamic stability of the cluster-CO complexes. The variations of adsorption energy, HOMO–LUMO gap, and NBO charge on CO fragment with the size of the clusters are reported. The CO adsorptions on Sn–Ge mixed clusters are confirmed by studying correlations among different parameters such as the increase in C–O bond length, the red shift in C–O stretching frequency, CO binding energy, changes in Gibbs free energy, and NBO charge on CO.