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Title: Ab initio simulations of minerals using localised basis sets
Author: Craig, M.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2001
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I have applied the recently developed ab initio simulation code, SIESTA, to a variety of studies of mineral systems. The code is designed to be capable of linear scaling, and promises the ability to simulate systems much larger than other ab initio methods. The SIESTA code is used in several studies of cation ordering to calculate small energy differences between structures in which cations are rearranged. The results are compared to those given by other ab initio methods, and by empirical potentials. SIESTA is found to be a useful tool, capable of improving on the accuracy of empirical potential methods, but able to tackle larger systems than traditional ab initio techniques. A study of the high-pressure phase transition in cristobalite is also used as a comparison between SIESTA and other methods. This study shows SIESTA to be capable of giving results comparable to the best ab initio methods, and the quality of results that can be expected at varying levels of convergence are demonstrated. A study of the adsorption of an adenine monolayer on a graphite surface demonstrates the ability of the code to perform calculations on a large unit cell practically, and illustrates some of the issues related to the Basis Set Superposition Error (BSSE) that is a disadvantage of the SIESTA method. A wide general study of adsorption of organic molecules on clay mineral surfaces shows some trends in binding energies of different molecules and cations, and considers the effect of absorbed water on the binding of a molecule. The practical utility of ab initio calculations for this type of study is demonstrated, raising the possibility of future work to fully understand the complex and environmentally important interactions between organic pollutant molecules and clay in soils.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available