First-principles calculations of optical properties: Application to silicon clusters

We have developed an ab initio method to calculate optical properties of crystals, clusters, and surfaces starting from their fully relaxed atomic configurations. The approach allows dealing with systems consisting of up to several hundred atoms per unit cell. We present results for silicon clusters consisting of 20, 60, and 70 atoms. We calculate the optical dielectric response function for clusters with different atomic structure. Quantum molecular dynamics simulations were performed to find metastable and equilibrium (lowest-energy) atomic configurations. We discuss the dependence of the optical properties of these silicon clusters on the number of atoms as well as on the specific structural properties. Comparison with theoretical and experimental results is also presented.