Electronic excitation energies of ZniSi clusters - art. no. 013201

Time-dependent density-functional theory (TDDFT) excitation energies are ca lculated for ZniSi global minima clusters, i = 1-9. The geometry of the glo bal minima is ringlike for i = 1-5 and three-dimensional (3D) spheroidlike for i = 6-9. In general, the calculated excitations happen from nonbonding p orbitals of sulfur. These orbitals are perpendicular to the molecular pla ne in the case of the rings, and normal to the spheroid surface for 3D clus ters. The calculated excitation energies are larger for ringlike clusters a s compared to 3D ones, with the excitation energies of the latter structure s lying close to the visible spectrum. The difference between Kohn-Sham eig envalues of the orbitals involved in the electronic excitations studied hav e also been compared with the TDDFT results of the corresponding excitation s for two approximate density functionals, i.e., MPW1PW91 and B3LYP, the la tter being more accurate. The B3LYP excitation energies calculated as the d ifference between Kohn-Sham eigenvalues of the orbitals involved in the exc itation have been found to be only 0.30-0.40 eV too high for the smaller 3D -like clusters. Moreover, they approach the TDDFT value as the cluster size increases. Therefore, this might be a practical approach to estimate excit ation energies of large ZniSi clusters.