Welcome!

Welcome to the homepage of Prof. Nick Besley

Welcome!

I am a Professor in Theoretical Chemistry here at the University of Nottingham. My group is interested in developing and applying quantum chemical methods to study a wide range of problems. For more information on my Research, see the "Research" sections.

I would welcome applications (from UK or EU) from students interested in a PhD position in my group.


Latest paper:

Density Functional Theory Based Methods for the Calculation of X-ray Spectroscopy

Acounts of Chemical Research

Nicholas A. Besley

Welcome to the University of Nottingham

The availability of new light sources combined with the realisation of the unique capabilities of spectroscopy in the X-ray region has driven tremendous advances in the field of X-ray spectroscopy. Currently, these techniques are emerging as powerful analytical tools for the study of a wide range of problems encompassing liquids, materials and biological systems. Time-resolved measurements add a further dimension to X-ray spectroscopy opening up the potential to resolve ultrafast chemical processes at an atomic level. X-ray spectroscopy en- compasses a range of techniques which provide complementary information, these include X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), X-ray emis- sion spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS). In many studies the interpretation of the experimental data relies upon calculations to enable the nature of underlying molecular structure, electronic structure and bonding to be revealed. Density functional theory (DFT) based methods are one of the most widely used methods for the simulation of X-ray spectra. In this Account, we focus on our recent contributions to the simulation of a range of X-ray spectroscopic techniques using DFT and linear-response time-dependent density functional theory (TDDFT) and show how these methods can provide a computational toolkit for the simulation of X-ray spectroscopy. The importance of the exchange-correlation functional for the calculation of XAS is discussed and the introduction of short-range corrected functionals described. The application of these calculations to study large systems through the use of efficient implementations of TDDFT will be highlighted, with the use of these methods illustrated through studies of ionic liquids and transition metal complexes. The extension of TDDFT to calculate XES through the use of a reference determinant for the core-ionised state will be described, and the factors that affect the accuracy of the computed spectra discussed. The application of these approaches will be illustrated through the study of a range of organic molecules and transition metal complexes, which also show how going beyond the dipole approximation in determining the transition intensities can be critical. The application of these approaches to the simulation of the RIXS spectrum of water will also be described, highlighting how ultra-fast dynamics on the femtoscale timescale are evident in the measured spectra. In these calculations the description of the core-ionised and core-excited states becomes increasingly important, and the role of the basis set in accurately describing these states will be explored.