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First-principles study of the phase diagram of Potassium

Boucher, Giulia; (2019) First-principles study of the phase diagram of Potassium. Doctoral thesis (Eng.D), UCL (University College London). Green open access

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Abstract

This thesis is a computer simulation project to calculate the phase diagram of potassium as a function of pressure from 0 to 100 GPa and temperature from 0 to 1200 K. The project required the application of both electronic structure techniques and classical molecular dynamics simulations to compute the free energies of solid and liquid phases. To compute the melting properties, the coexistence was used, either with a classical potential fitted to the ab initio data or directly with the ab initio potential. Tests were also carried out using the Z method, however, this method cannot compute melting properties but can provide an estimate of the upper bound of the melting temperature. The phase transitions of the solid structures of potassium were determined from 0 to 100 GPa at temperatures ranging from 0 to 450K using first-principles calculations of the free energies. The calculations were carried out within the density functional theory framework with the generalised gradient approximation and the projector augmented wave method as implemented in VASP. The quasi-harmonic contribution to the free energy of the solids was calculated using the small displacement method. To determine the melting temperature of each solid phase of potassium, the coexistence method with a potential was used but proved unsuccessful for most phases. Therefore, the direct coexistence was used but was deemed computationally too expensive. As aforementionned, the Z method was tested in order to obtain an approximation of the melting temperature and assess the performance of the method.

Type: Thesis (Doctoral)
Qualification: Eng.D
Title: First-principles study of the phase diagram of Potassium
Event: UCL (University College London)
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2019. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms.
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: https://discovery.ucl.ac.uk/id/eprint/10068831
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