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Title: Linear-scaling density functional theory and theoretical electron energy loss spectroscopy investigations of surfaces and defects in nanomaterials
Author: Tait, Edward William
ISNI:       0000 0004 7961 8419
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2019
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This work presents a method for the computation of electron energy loss spectra for large systems using the onetep code. The foundations of density functional theory will be discussed, with a focus on the linear scaling methods employed by onetep. A method for the prediction of spectra will be shown, with emphasis on the construction of the matrix elements needed. This method is tested against both other DFT codes and experiment. Once the ability of onetep to predict EEL spectra has been established the code is used to predict the spectra associated with oxygen vacancy defects in the anatase (101) surface. These spectra are found to agree with the limited experimental data available. EEL spectra for nitrogen dopants in anatase are also predicted, based on literature geometries for these. The energetics of the oxygen vacancy is also explored, using the ability of onetep to perform calculations on large cells to address elastic finite size effects and employing a correction scheme to remove electrostatic finite size effects. Finally, the properties of an extended grain boundaries defect in GaAs were investigated, focussing on properties relevant for optoelectronics.
Supervisor: Hine, Nicholas ; Ducati, Caterina Sponsor: EPSRC ; University of Cambridge
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: EELS ; Electron Energy Loss Spectroscopy ; ONETEP ; DFT ; Linear Scaling ; Density Functional Theory ; Anatase ; Titanium Dioxide ; LS-DFT ; Defect ; Surface Defect ; Formation Energy