"The development of ultrafast experimental techniques with femtosecond time resolution is driving the need for deeper theoretical understanding of how intense optical excitation can alter the interatomic forces, drive atomic motion and effect structural changes in materials. The main objective of this project is to extend the scope of electronic structure computational methods, allowing us to quantitatively simulate (without phenomenological parameters) the coupled electronic and atomic dynamics in highly photoexcited materials on a picosecond and sub-picosecond timescale. We will use these new methods to calculate the transfer of energy from electronic states to the lattice vibrations in photoexcited GaAs and to follow the redistribution of vibrational energy through to its ultimate thermalisation in the lattice. We will compare our predictions of electronic distributions and vibrational motion with those measured by our collaborators, using time-resolved photoemission and x-ray diffraction, allowing us to benchmark the effectiveness of our theoretical approach. The understanding of energy relaxation and transfer following optical excitation underpins a variety of technologically important processes: e.g. the ultrafast response of optically active components in high-speed telecommunications and, in the field of renewable energy, the initial stages of photocatalysis or optical absorption in solar cells. To support advances in these areas, it is important to develop predictive methods for modelling the behaviour of optically excited materials at an atomic level on very short time scales. In delivering these predictive methods and by the virtue of the applicant's expertise in electronic structure theory and the emerging field of ultrafast electron and phonon dynamics, this project will enhance EU scientific excellence and competitiveness."