Modelling

Modelling and simulation is a central part of our research. 

We use quantum mechanics (density functional theory) to simulate materials, defects and experimental data.  In all cases, the aim of the modelling is to solve a Materials Science problem.  Often simulated data is used to help interpret experiment to tell us more about a material. 

All members of the group use modelling to some extent in their research.  Some members of the research group use simulation to explain the experimental data they have obtained, others are focussed on developing methods for simulating experimental data. 

Current projects:

Exploring low energy excitations with electron microscopy

A new generation of electron microscopes are able to combine atomic resolution imaging with high resolution electron energy loss spectroscopy, allowing vibrational spectroscopy at atomic resolution.  

In parallel with developments in experimental capabilities, there have also been theoretical developments to understand the new experimental data.  Sabrina Wang is working a theory of vibrations in molecular crystals

Modelling high-precision TEM phase imaging with Density Functional Theory

Electron ptychography data from an electron microscope has the potential to tell us a lot about a material, but the extraction of information can require comparison with experiment.  Ewan Richardson and Yiran Wang working on simulating ptychography data using density functional theory.  

Previous Publications:

Momentum-resolved phonon spectroscopy in the electron microscope

Vibrations of atoms within a crystal can be described by phonons.  

Momentum-resolved phonon spectroscopy carried out within the electron microscope is a new experimental technique which allows the collection of data similar to that produced by inelastic neutron or x-ray scattering but it can be done on volumes of materials up to 20 orders of magnitude smaller.

The development of this technique and a theoretical model which allows spectra to be simulated entirely from first principles calculations can be found in Hage et al., Science Advances, 4 (2018) eaar7495 and Nicholls et al., Phys Rev B, 99 (2019) 094105

Code development:

OptaDOS

Rebecca Nicholls is one of the developers of OptaDOS, a code developed for predicting optical and core-level spectroscopy.  The predicted spectra can be used to interpret spectra from electrons or X-rays.  OptaDOS is an open source code which can be freely downloaded by the scientific community.