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Abstract

There is growing evidence to suggest that small energetically favourable clusters play an important role in the thermodynamics and dynamics of liquids. However, identifying and quantifying favoured local structures (FLS) in real liquids remains a challenge. Ronceray and Harrowell[ EPL, 96 (2011) 36005] developed a simple spin lattice model that explore the effects such structures have on the properties of the liquid and their ability to freeze. By selecting different FLS, they found the model froze to an array of different crystal structures with varying unit cell sizes and complexities through a range of strong and weak first order transitions. This thesis explores how complex structures are formed through nucleation and contrasts the nucleation mechanism of the {1,5} FLS model, which exhibits a weak first order transition, with that of the {3,3} FLS model, which freezes through a strong first order transition. Monte Carlo simulation and the mean first passage time method were employed to calculate the nucleation rate and identify the nature of the critical nucleus for the FLS model systems. The {1,5} FLS system accumulates a significant amount of solid-like structure in the metastable liquid phase prior to freezing. As a result, the supercooled liquid contains large equilibrium solid-like clusters that fluctuate in size prior to nucleation. After visualization of the spins, the {1,5} FLS system showed that the system forms a structure close to that of the crystal before crystallization. In contrast, the {3,3} FLS system forms most of its structure during the transition process. The energy barrier for the {3,3} FLS system was found to be higher than that observed for the {1,5} FLS system. This work examines the role the symmetry and structural correlation of the FLS might play in the different freezing and nucleation behaviours of the two systems.