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Title: Development and application of path integral methods to study nuclear quantum effects in aqueous systems
Author: Buxton, Samuel
ISNI:       0000 0004 9358 1210
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2019
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Nuclear quantum effects have been shown to play a large role in defining the properties of chemical systems. However including these in computational simulations for example using path integral methods is far more computationally expensive than a classical simulation where these effects are ignored. This is because the number of individual force calculations is greatly increased when using a path integral method. This means that for some systems and system sizes it is difficult to computationally evaluate fully quantum properties. To address this, methods have been developed that can accelerate this simulations with minimal loss of accuracy, however the most popular methods all suffer from drawbacks which limits their application to certain types of system. This work presents a novel method for increasing the speed of path integral simulations that employs Kernel-Ridge Regression to enable fewer individual force calculations during the simulation while maintaining accuracy. The main advantage of this method lies in its ability to be applied to any system of interest with no conditions or prior assumptions about the potential energy surface. Results for this method are very positive when applied to two systems where quantum effects are prevalent, liquid water and para-hydrogen. In addition to this work, an investigation is carried out into the role of nuclear quantum effects in the free energies of hexagonal and cubic ice, as hexagonal is only more stable by ≈ 40 J mol⁻¹ and it has not been shown what causes this extra stability, as the two polymorphs have almost identical properties and differ only in their stacking arrangement. Our results show that the inclusion of nuclear quantum effects stabilises hexagonal ice relative to cubic ice, leading to a greater free energy difference more in line with experimental values. Finally we examine how nuclear quantum effects play a role in the surface properties of small water droplets and how ion diffusion is affected, as there is interest in how these droplets may play a role in or catalyse chemical reactions.
Supervisor: Not available Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics ; QD Chemistry