Atomic scale structures are studied using first principles or ab initio simulations. We first review the formalism required for a typical calculation and then proceed to examine a few applications. All the simulations were performed using plane wave based pseudopotential methods and by a direct minimization of the Kohn-Sham total energy functional. / Using this method, we have investigated the effect of impurity atoms like boron, sulphur and phosphorous on the adhesive properties of two aluminium minimum slabs. We found that both sulphur and phosphorous (both substitutional impurities) decreased the adhesive energy and the interfacial strength, while boron (an interstitial impurity) increased the interfacial strength marginally. It was also found that the impurities act as spacers and increase the interfacial spacing. This increase was found to increase with atomic size. These observations are consistent with experimental work. / We have also investigated the possibility of using orbital-free kinetic energy functionals in ab initio simulations. Various functionals, their limiting forms and response properties were studied. The results obtained using this method agree well with full Kohn-Sham calculations. This was demonstrated using a variety of systems (Si clusters, H$ vert$Si(100), c-Si). The excellent scaling properties of the method was illustrated with a simulation of the interactions between a tip and substrate (150 atoms). The normal forces experienced by the small cluster serving as the tip were used to map out the top surface of the substrate. An ad hoc scheme to incorporate pseudopotential non-locality into the orbital-free formalism was also proposed and tested.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.39910 |
| Date | January 1995 |
| Creators | Govind, Niranjan |
| Contributors | Guo, Hong (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Physics.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001484921, proquestno: NN12374, Theses scanned by UMI/ProQuest. |
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