Atomic and electronic structure of silicon clusters at finite temperature

Predicting the atomic and electronic properties of clusters is one of the outstanding problems in materials science. The numerous degrees of freedom and low symmetry of clusters make it difficult to perform effective searches for the ground state structure and the corresponding electronic structure for the cluster of interest. Even if an effective procedure can be devised to predict the ground state structure, questions can arise about the relevancy of the structure at finite temperatures. Kinetic effects and non-equilibrium structures may dominate the structural configurations present in clusters created under laboratory conditions. In this article, methods for determining the structure and electronic properties of clusters are reviewed. The emphasis is on ab initio methods. As a specific example, the electronic spectra of electrically charged small silicon clusters are calculated from quantum simulations at finite temperature. These calculations are shown to yield an accurate description of existing photoelectron data on negatively charged clusters. The detailed agreement between theoretical and experimental features and the high sensitivity of the electronic spectra to the cluster geometry can be exploited to identify the relevant isomers present under experimental conditions. The results show the importance of atomic relaxation within the charged cluster, as opposed to photoemission-induced relaxation effects, in determining the observed spectra.