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Title: Pressure-induced structural transformations in nanomaterials : towards high accuracy large length- and time-scale simulations
Author: Corsini, Niccolo
ISNI:       0000 0004 5989 5603
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2015
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The study of pressure-induced structural transformations in nanomaterials is both of fundamental and technological importance. Accurate simulations of these transformations are challenging because large length- and time-scales have to be simulated to make contact with experiments whilst retaining the atomic detail for a faithful description. In this thesis, both classical and quantum mechanical techniques are used to model pressure-induced structural transformations in realistic Si, Ge and CdS nanocrystals and comparison made to experiment where possible. We implement an electronic enthalpy method within the linear-scaling density-functional theory ONETEP code and, after introducing an approach for calibrating the volume definition, investigate the size-dependent pressure-induced amorphisation and polyamorphic transformations in hydrogenated Si and Ge nanocrystals. For the latter, we elucidate the surface-induced amorphisation and the new high-density amorphous metallic Ge phase observed experimentally. We combine this method with the projector-augmented wave and time-dependent density-functional theory methods to study the size and ligand dependence of deformation and optoelectronic properties of CdS nanocrystals with pressure. We develop a novel classical parametrisation for the simulation of bare and ligated CdS nanocrystals immersed in a pressure-transmitting medium and investigate their transformation under pressure using classical molecular dynamics and the metadynamics method for accelerating rare events. The resulting polymorphic transformation and pressure-induced amorphisation are analysed in detail.
Supervisor: Haynes, Peter Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available