Madeleine Meyer

Electronic structure of stannous oxide

Abstract We present an ab initio study of the electronic structure of SnO. Density functional theory in the local density approximation (DFT-LDA) is used in conjunction with carefully tested smooth pseudopotentials. Total energies and charge densities are calculated and analysed as a function of the atomic geometry, with a particular emphasis on the importance of low-charge-density contributions to the interlayer cohesion. SnO 2 has already been studied in the past and is used for comparison.

Molecular dynamics simulation of the atomic structure of a NiO tilt grain boundary at high temperature

The detailed atomic structure of the 5(310)[001] tilt grain boundary is still the subject of controversy since the structures deduced from high-resolution electron microscopy (HREM) experiments differ from those derived from static calculations. The presence of defects combined with the effects of temperature have been proposed as possible reasons for this discrepancy. To elucidate this question we examined several possible configurations of the grain boundary structural unit in which we incorporated defects. Some of these configurations were selected after energy minimization at T = 0 K and then studied at high temperature. We chose the lowest energy configurations, in which there are still some defects remaining after relaxation, to perform high temperature simulations using constant temperature molecular dynamics. The detailed analysis of the results shows that the defects have a tendency to agglomerate; in some cases this agglomeration can even locally modify the periodicity of the grain boundary. Using the average location of the atoms resulting from the high-temperature simulations, we performed HREM image simulations. Several images present features which are also observed in the experimental HREM images. Indeed the degree of agreement between our results and the HREM experimental images is improved with respect to the structures resulting from the calculations performed on configurations without defects.