Quantitative Convergent Beam Electron Diffraction and Charge Density Studies
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- Institutt for fysikk 
Very accurate low-order structure factors have been measured in copper, magnesium and strontium titanate using quantitative convergent beam electron diffraction (QCBED). The charge density distribution in these materials has been studied using the measured structure factors. The results have also been compared to ab initio density functional theory (DFT) calculations. In the case of copper, we combined our low-order structure factors with higher order γ-ray structure factors, in order to obtain a larger experimental data set for maximum entropy and multipole analysis. The results show that bond formation induces a large change in the 3d orbital radial function. As expected for metallic bonding, no asphericity of the orbitals has been observed. These results are in perfect agreement with DFT calculations. For magnesium it was shown that the anisotropic displacement parameters could be determined accurately from the low order QCBED data, if structure factors from DFT calculations were used as a static lattice reference. This data set was combined with X-ray structure factor measurements and used to test some commonly used DFT functionals and self interaction correction (SIC) schemes. It was found that the local density approximation combined with the SIC of Lundin and Eriksson (2001) gave the best agreement with experiments. Using this functional no non-nuclear maximum was found in beryllium, but not in magnesium.
Has partsFriis, J; Jiang, B; Spence, JCH; Holmestad, R. Quantitative Convergent Beam Electron Diffraction Measurements of Low-Order Structure Factors in Copper. Microscopy and Microanalysis. 9(5): 379-389, 2003.
Jiang, B; Zuo, J-M; Friis, J; Spence, JCH. On the Consistency of QCBED Structure Factor Measurements for TiO2 (Rutile). Microscopy and Microanalysis. 9(5): 457-467, 2003.
Friis, J; Martinsen, K; Holmestad, R. Retrieval of anisotropic displacement parameters in Mg from convergent bean electroni diffraction. EMAG Proceedings 2003. Inst. Phys. Conf. Ser.(165), 2003.
Friis, J; Madsen, GKH; Larsen, FK; Jiang, B; Martinsen, K; Holmestad, R. Magnesium: Comparison of density functional theory calculations with electron and x-ray diffraction experiments. J. Chem. Phys.. 119(21): 11359-11366, 2003.
Friis, J; Jiang, B; Marthinsen, K; Holmestad, R. A study of charge density in copper. Acta Cryst.. A61(2): 223-230, 2005.
Jiang, B; Friis, J; Holmestad, R; Zuo, JM; O'Keeffe, M; Spence, JCH. Electron density and implication for bonding in Cu. Physical Review B (Condensed Matter and Materials Physics. 69: 245110, 2004.