I completed a masters degree (MPhys) in theoretical physics at the university of York in 2014. While at York I was supervised by Prof. Rex Godby, and helped develop the iDEA code. This code solves the exact many-electron Schrodinger equation and then reverse engineers the exact Kohn-Sham orbitals that represent the system. It was at this time that I developed an interest in density functional theory (DFT), which is now my main research area.
Accurately calculating the properties of charged point defects in materials is a challenge using DFT. An understanding of the properties of such defects is vital to predicting the performance of electronic devices, as electric currents can charge defects and break the device. Periodic DFT calculations treat neutral defects well, but the long range nature of the Coulomb interaction prevents charged defects from being separated from their periodic images, leading to unwanted interactions. Classical electrostatics can be used to model and remove these extra interactions and get meaningful formation energies. We work on extending these methods to surfaces and interfaces. As an example, the charge density contained in a Vcl defect in a +1 charge state is shown, when the defect is placed at a (001) surface termination of NaCl crystal.
These interfaces show many technologically useful applications, but are hard to model using DFT, as standard methods cannot treat both insulators and metals accurately. We use the auxiliary density matrix method (ADMM) to only apply Fock exchange to the oxide layer. The example shown is MgO grown on the (001) surface of Ag. In this case, the interface between the materials is very clean, allowing the partitioning of the system in this way.
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