Computational X-ray Spectroscopy

In recent years, advances in X-ray light sources have led to resurgence in interest in spectroscopy in the X-ray region, and the development of X-ray free-electron lasers that can deliver short femtosecond pulses of hard X-rays has opened up a new vista in time-resolved X-ray absorption measurements that hold the promise of resolving ultrafast chemical processes at an atomic level. The chemical selectivity of these techniques make it ideal as a local probe, providing both the local geometric structure and the electronic environment around a given atom. A common aspect of many studies exploiting these techniques is the use of computational simulations to interpret and analyse the experimental data. This has led to a pressing need for quantitatively accurate calculations of X-ray spectroscopy that can be applied to a wide spectrum of problems. However, the development of methods to simulate spectroscopy in the X-ray region has lagged behind comparable methods able to treat spectroscopy in the UV region, and currently there is no software available that is able to provide quantitatively accurate X-ray absorption and emission spectra for a wide range of systems.


This proposal aims to re-address this balance through the development of specifically designed functionality for the computation of X-ray absorption and emission spectroscopies within the framework of time-dependent density functional theory. This will result in software capable of providing accurate simulations of X-ray absorption and emission spectra that can be applied to a diverse range of systems that can be used by a non-expert user and is capable of treating very large molecules and excitations from transition metal elements. A complementary strand of the work will be to exploit the techniques developed to address systems of key interest, including the interpretation of the X-ray spectroscopic measurements of liquid water, ionic liquids and picosecond X-ray absorption spectroscopy of photo-excited transition metal complexes. This aspect of the project will be enabled through the award of a PhD studentship funded by the School of Chemistry at Nottingham.

The 2012 report 'UK e-Infrastructure Strategy for Science and Business' commissioned by The Department for Business, Innovation & Skills (BIS) highlighted the importance of computation and simulation in scientific process and innovation and led the EPSRC to recognise that the large suite of codes used in research therefore needs to be regarded as a research infrastructure in its own right, requiring support and maintenance along the innovation chain, and throughout its lifecycle. The proposal fits into this framework and outlines a detailed programme for the development and implementation of computational methodologies for the simulation of X-ray absorption and X-ray emission spectroscopies. The primary impact of the work will be amongst the academic and industrial research communities exploiting X-ray spectroscopies in their work. These researchers will benefit from the greater accuracy and much wider range of systems that will be opened up for study by the new software. The software will be readily available through the Q-Chem and Spartan software packages and will be designed to be used by a non-expert user.


Furthermore, the project will address specific scientific problems including interpreting the X-ray spectroscopy of liquid water and understanding the implications for its structure, the study of ionic liquids and the X-ray absorption spectroscopy of photo-excited transition metal complexes building on International and National collaborations resulting in impact in these areas of research. The project will provide excellent training in software development and High Performance Computing for the appointed PDRA and graduate student. Computational science has a proven track record in developing both the technical and soft skills of its practitioners, so giving access to numerous high-level career pathways either within or outside of academia. There will be considerable secondary impact that will stem from the scientific projects that exploit the new software which can be from across the spectrum of work in the remit of EPSRC encompassing many of the Grand Challenges.