The Shape of Copper Oxide Clusters Under Oxygen Excess: A Genetic Algorithm Search
Examensarbete för masterexamen
Applied physics (MPAPP), MSc
The stability of copper oxide clusters was investigated using density functional theory (DFT) where the exchange-correlation was described by the Perdew-Burke-Ernzerhof generalized gradient approximation. In particular, the Cu1–3O1–6 and [Cu6O3–9]+/− clusters were investigated. To estimate the stability, the free energy of the oxidized cluster was compared to the free energies of the corresponding bare cluster and gas phase molecular oxygen. A genetic algorithm was used to find the lowest energy shapes of the clusters. For the neutral clusters, the structures found by the genetic algorithm were compared to structures found in previous theoretical studies. In many cases the results agreed. In those cases they did not, the cause of the difference was ascribed to the different exchange-correlation functionals that were used in the DFT calculations. Regarding the stability, many of the oxygen-rich clusters had a low free energy at room temperature. The results for the charged clusters were compared to experiments measuring the relative abundance of copper oxide clusters of different compositions. The trends found in this thesis are similar to those found experimentally. For example, at room temperature, experiments found [Cu6O7]+ to be the most abundant composition for the cations. This is in good agreement with the results found in this thesis. Similarly for the anions, theoretical and experimental results agree on [Cu6O5]− being the most stable composition.
Fysik , Physical Sciences