Condensed-Matter Physics & Materials Science Seminar

Weidong Luo
Department of Physics and Astronomy, Vanderbilt University
Materials Science and Technology Division, Oak Ridge National Laboratory

The combination of density-functional theory (DFT), Z-contrast imaging and electron energy-loss spectroscopy is a very powerful approach to address and resolve problems in diverse materials systems. In this talk, I will discuss several theoretical studies using DFT within this synergistic approach. First, I will talk about benchmark DFT calculations for the ground-state structural, electronic and magnetic properties for both undoped and doped CaMnO3. The results are in excellent agreement with available data. More specifically, the DFT results predict two inequivalent Mn atoms in both 0.33 and 0.5 electron-doped CaMnO3, in agreement with experimental evidence of Mn+3/Mn+4 oxidation state ordering. I will also discuss the magnetic properties of La2/3Ca1/3MnO3 at the La2/3Ca1/3MnO3/YBa2Cu3O7 interface, giving an explanation to the magnetic “dead layer” behavior observed experimentally. Next, I will present spin-polarized DFT calculations for Au nanoclusters. The highest-occupied energy levels in some Au nanoclusters are highly degenerate and partially filled by s electrons. The nanoclusters behave like “superatoms” with spins aligned according to Hund’s rule, resulting in unexpected magnetic ground states. Finally, point defect configurations of Au atoms inside Si nanowires will be discussed. We identify a substitutional and three distinct interstitial configurations, one of which has not been previously identified. The observed densities of the various configurations are consistent with the formation energies calculated using DFT.