First principles calculations, using the density-functional theory and particularly the local density approximation (LDA), have achieved remarkable success in studying the properties of solid state systems. Although the basic results of these calculations are the electronic structures (eigenvalues, eigenfunctions, etc.) and the total energy of ground state, many other related physical properties can be deduced from them by investigating their response under external perturbations. Using the linear response method with linearized-augmented-plane-wave (LAPW) basis, we have calculated lattice dynamical properties of important semiconductors CuCl, SiC and ferroelectric KNbO{dollar}\sb3.{dollar} CuCl is known to exhibit large anharmonic effects and possibly a complicated multi-well Born Oppenheimer surface reminiscent of the instabilities in perovskite ferroelectrics and the high-temperature cuprate superconductors. However, we have determined its phonon dispersion from first-principles calculations and find it to be in good agreement with the low temperature experimental results. For zincblende SiC, the calculated phonon dispersions, Grunensen's parameters, dielectric constant, Born effective charge, elastic constants, and the equation of state agree very well with the available experimental data. Additionally, we find that its dielectric constant decreases with pressure and Born effective charge increases with pressure up to 80 GPa without any saturation, calling into question the recent interpretation of experimental results to the contrary. Our calculations for KNbO{dollar}\sb3{dollar} find unusually large Born effective charges on Nb and O that originate from the strong covalent interactions between Nb 4d and O 2p orbitals. The Born effective charges and dielectric tensors are found to change up to 20% from the cubic structure to the rhombohedral structure, demonstrating that the polarizability of the perovskite ferroelectrics is very sensitive to the small atomic displacements involved in the transitions. The phonon modes for the cubic and rhombohedral structures are also calculated and their implications are discussed.
| Identifer | oai:union.ndltd.org:wm.edu/oai:scholarworks.wm.edu:etd-3784 |
| Date | 01 January 1995 |
| Creators | Wang, Cheng-Zhang |
| Publisher | W&M ScholarWorks |
| Source Sets | William and Mary |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Dissertations, Theses, and Masters Projects |
| Rights | © The Author |
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