eprintid: 10068831 rev_number: 23 eprint_status: archive userid: 608 dir: disk0/10/06/88/31 datestamp: 2019-03-21 18:23:04 lastmod: 2019-03-21 18:23:04 status_changed: 2019-03-21 18:23:04 type: thesis metadata_visibility: show creators_name: Boucher, Giulia title: First-principles study of the phase diagram of Potassium ispublished: unpub divisions: A01 divisions: B04 divisions: C06 divisions: F56 note: 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. 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. date: 2019-02-28 date_type: published oa_status: green full_text_type: other thesis_class: doctoral_open thesis_award: Eng.D language: eng thesis_view: UCL_Thesis primo: open primo_central: open_green verified: verified_manual elements_id: 1632923 lyricists_name: Boucher, Giulia lyricists_id: BOUCH76 actors_name: Boucher, Giulia actors_name: Allington-Smith, Dominic actors_id: BOUCH76 actors_id: DAALL44 actors_role: owner actors_role: impersonator full_text_status: public pages: 199 event_title: UCL (University College London) institution: UCL (University College London) department: Chemistry thesis_type: Doctoral citation: Boucher, Giulia; (2019) First-principles study of the phase diagram of Potassium. Doctoral thesis (Eng.D), UCL (University College London). Green open access document_url: https://discovery.ucl.ac.uk/id/eprint/10068831/1/Boucher_10068831_thesis.pdf