Theoretical study of structural, electronic, and optical properties of ZnmSen clusters

We present density-functional theoretical results of structural, electronic, and optical properties of ligand-free ZnmSen clusters as a function of size of the cluster. We have optimized the structure, whereby our initial structures are spherical parts of either zinc blende or wurtzite crystal structure and we have studied systems up to almost 200 atoms. The calculations were performed by using density-functional tight-binding (DFTB) method. The results include the radial distribution of atoms and of Mulliken populations, the electronic energy levels (in particular the highest occupied molecular orbital and lowest unoccupied molecular orbital), the band gap and the stability as a function of size and composition. In addition to structural and electronic properties we present electronic excitation spectra obtained from time-dependent density functional response theory.