Phil's Research Interests

My research involves the use of density functional theory (DFT) to perform computer simulations of materials and chemical systems and processes on an atomic scale. These calculations treat the electrons quantum mechanically, though the nuclei are usually treated as classical point particles. I am part of the condensed matter dynamics group, and employed by the United Kingdom Car-Parrinello Consortium.

DFT is a reformulation of quantum mechanics in terms of electron density rather than the many-electron wavefunction. This reformulation leads to a huge reduction in the computational complexity of quantum mechanical simulations, so that it is now possible to predict many properties of matter from first principles (also referred to as ab initio).

Practical DFT calculations are only possible because of the development of efficient, robust computer programs to simulate general materials systems. My research focuses on developing and optimising algorithms and computational methods in the DFT program CASTEP. The main goal of this research is to make these calculations as robust and efficient as possible, regardless of the material or chemical being simulated, or the computer used to run the program.

These ambitious aims require developments in a wide variety of fields, from non-linear optimisation and eigenvalue solvers to parallel programming, all underpinned by good software engineering and design principles to ensure the program is as bug-free, portable and maintainable as possible.

In addition to software and methodological development, I also use CASTEP to try to understand different behaviours and phenomena observed in experiments. Recent applications include simulations of half-metallic Heusler alloys for use in future spintronic devices, and predicted electron-energy loss spectra (EELS) from graphene nanoribbons (see my publications for more details).

Fundamentals of DFT

I am especially interested in the fundamental algorithms and techniques used to find the groundstate electronic density, especially for metallic systems. The algorithmic areas I have been working on recently are:

• Ensemble density functional theory
• Density mixing methods
• Preconditioning for electronic structure optimisation problem
• Subspace minimisation techniques
• Berry phase and applied electric field

These developments are based on the CASTEP simulation software, and are supported by the CASTEP Development Group (CDG) and the UK Car-Parrinello Consortium.

Applications of DFT

As well as developing and writing algorithms to perform DFT calculations, I also apply DFT to a wide range of real-world problems. Some of my more recent projects include:

• Half-metallic Heusler alloys
• Nanoscale growth of polar oxides
• Characterisation of nanomaterials
• Band offset calculations in semiconductor junctions
• I-V modelling of Schottky barriers

Information on some of these can be found in my recent publications.