Ab Initio Theoretical Study of Phonons in Metals and Alloys under Extreme High-P,T Conditions
Supervisors: Professor Paul McMillan & Dr Furio Cora
This project will use advanced ab initio simulation techniques to study phonons in selected metals and alloys as a function of pressure and temperature in order to rationalise and predict their thermophysical behaviour, as well as phase transitions including melting. The systems to be studied will be chosen to match parallel experimental investigations being carried within the ISP at UCL using diamond anvil cell techniques. They will include important hexagonal and cubic metallic structures Sn, Pb, Ti, Ta and Ti-Al-V alloys for which accurate and reliable thermodynamic data are needed for future modelling and simulation studies.
Ab initio calculations will be carried out using established density functional (DFT) theoretical techniques including plane wave and ultrasoft pseudopotential methods and first principles molecular dynamics (MD). The main goals of the proposed PhD project will be to study the pressure dependence of the phonon density of states and vibrational anharmonicity, to help interpret, complement and extrapolate newly obtained experimental results, and to extract useful therodynamic parameters that can link static vs shock studies and provide input data for large-scale materials properties simulations.
Experimental studies examine hcp metals like Sn and Ti that exhibit Raman active modes at the Brillouin zone (BZ) centre. The ab initio calculations will provide information on the full vibrational density of states (VDOS) at high pressure, with useful calibrations and checks provided by the experimental data. The calculated VDOS and phonon dispersion relations will then be used to derive important properties such as the heat capacity, entropy and thermal conductivity under high P conditions.
Later experiments will focus on cubic metals that normally have no first order Raman spectrum. However it is observed that formation of disordered cubic alloys (including TiAlxVy) results in 'activation' of the VDOS throughout the BZ that can be studied using Raman spectroscopy, and these can be measured to magabar pressures in the diamond anvil cell. However we must have ab initiopredictions of the VDOS to interpret, validate and complete the experimental results and derive the thermodynamic parameters. That will be a goal of the theoretical PhD project.