White, Nigel John;
(2002)
Interionic potentials and the compressible ion model.
Masters thesis (M.Phil), UCL (University College London).
Preview |
Text
Interionic_potentials_and_the_.pdf Download (7MB) | Preview |
Abstract
The Compressible Ion Model (CIM) is described and used to model LiF and the rocksalt oxides SrO and BaO in the rocksalt (B1), caesium chloride (B2) and zinc blende (B3) structures. The CIM is a fully ionic model that includes the effects of the ionic environment by allowing the anion to compress relative to the free ion when inside the crystal. This process gives rise to a rearrangement energy. Given the wavefunctions resulting from this modification, this energy and the short-range pair interactions are calculated within Dirac-Fock theory, thus excluding the effects of electron correlation. This constitutes the major portion of the cohesive energy. The effects of electron correlation are then included through a local density approximation to density functional theory for the correlation contribution to the rearrangement energy and the short-range pair interactions. The dispersion interaction for the crystal is evaluated with the inclusion of the damping that is required due to the overlap of the ion wavefunctions. The model correctly predicts the rocksalt (B1) structure as the most stable for all of the materials tested and appears to show good transferability across the structures. Predictions for the equilibrium cation-anion separation and cohesive energy are made and for LiF show excellent agreement with experiment. This agreement decreases for SrO and BaO, with a comparison to previous work suggesting a possible difficulty in the model for larger cations in the series MgO to BaO. Each energy component making up the cohesive energy is reported, providing the ab initio data and insight that would be required for an attempt to construct a physically transparent parameterised potential model based on the CIM.
| Type: | Thesis (Masters) |
|---|---|
| Qualification: | M.Phil |
| Title: | Interionic potentials and the compressible ion model |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Thesis digitised by ProQuest. |
| Keywords: | Pure sciences; Compressible ion model |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10103234 |
Archive Staff Only
 |
View Item |
