Armoured: Atomic R-matrix Method For Relativistic Dynamics

In order to 'view' electrons in the atom, we need to be able to describe their motion on a time-scale comparable to the interactions themselves. This is akin to taking a photograph- the faster an object is moving, the shorter the exposure time required to capture it. The process of harmonic generation- where an electron in an atom is driven by a laser field in such a way as it re-emits high harmonics of the laser light- has provided a unique tool for probing atomic and molecular structure- allowing the imaging of molecular orbitals and even videos of chemical reactions taking place. While this field of attosecond physics (1 attosecond = 1 billionth of a billionth of a second) is well established, the theoretical description and computational models of the underlying processes are underdeveloped.

In order to fully describe the fundamental dynamics of laser driven electrons in the atom we need to consider not just the effect of the laser field, nor even simply the net effect of the electrons, we must also describe the complex interactions between the many electrons. In order to facilitate this description in a computationally tractable way we have developed time-dependent R-matrix theory (TDRM), and associated computer codes. The theory makes use of an R-matrix division of configuration space in order to simplify the calculations without neglecting important multielectron effects.

It is our intention to extend the TDRM technique to describe relativistic effects in ultrafast processes. The spin-orbit interaction, wherein an electron's intrinsic (spin) and orbital angular momenta interfere to change its behaviour, gives rise to fine structure splittings in atomic energy levels. The transitions of electrons between these levels occurs on a time-scale governed by the energy gap. For heavier elements such as krypton and xenon this time-scale is of the order of a few femtoseconds- and so dynamics can evolve within a laser pulse. By opening up new electron-emission channels, and changing the selection rules for electron transitions, the spin-orbit effect can significantly alter the fundamental processes of attosecond physics- ionisation, harmonic generation etc. Hence, interesting new dynamics can be observed on the atomic scale. By using the TDRM method we will be able to model these dynamics from first principles, thus giving an unparallelled insight into some of the most fundamental physical processes in atomic science.

FUNDAMENTAL SCIENCE

Understanding of fundamental phenomena

The calculations we perform, and the scientific problems we will address will directly inform our understanding of the very fundamental fields of ultrafast electron dynamics, electron correlation effects and atomic structure.

Improved understanding in these areas will directly inform:

- Astrophysics: atomic opacities, scattering cross sections (CS)
- Materials science: electron transport
- Fusion energy: Scattering CS
- Laser physics: electron dynamics, ultrafast phenomena, high harmonic generation
- Radiation damage: electron dynamics in molecular systems
- Plasma physics: Scattering CS

Improve and develop experimental techniques

We will directly address high harmonic spectroscopy and attosecond transient absorption spectroscopy. Performing HHG calculations, and thereby uncovering possible improvements in efficiency or generality of the process impacts on

- XUV-initiated HHG
- Attosecond laser pulse generation
- Multidimensional spectroscopy
- Free-electron laser science

The proposed improvements to the computational approaches we propose will impact on ongoing research into fusion energy.

COMPUTATIONAL PHYSICS

Understand, improve and enhance computational methods

The specific area of computational physics we address will be ab-initio modelling of multi-electron systems. However, the techniques we use:

- novel mixed basis-set/finite difference techniques
- mixed (shared/distributed) memory parallelism
- novel hardware for HPC (deployment of RMT on Intel Xeon Phi architecture)

are more generally applicable in a variety of areas using HPC.

ECONOMIC AND SOCIETAL

Improved understanding of light mediated charge transfer, allows better understanding and control of

- vision
- photosynthesis
- nano-scale electronics
- high-speed electronics
- the manufacture and efficient operation of photovoltaic cells

with clear implications for medicine, human and plant biology, emerging technologies and renewable energy respectively.

Direct engagement with two ongoing projects in magnetic confinement fusion has important long term consequences for clean energy, and knock-on impacts for defence and security.

The high performance computing aspects of the work will inform the development and design of new HPC facilities. The testing of novel HPC technologies (at present the Intel Xeon Phi coprocessor) forms an important part of our engagement with the Irish Centre for High End Computing. This has far reaching implications for all the research areas which use HPC worldwide including

- meteorology
- medicine
- aerospace engineering
- renewable energy research
- defence

We will directly engage the public to improve understanding and awareness of fundamental science. In particular, we will create video introductions to the areas of

- ultrafast physics
- supercomputing for science

By directly engaging with three companies we will establish new connections and develop existing links between fundamental science and industry in the areas of

- plasma physics (via Quantemol)
- laser physics and metrology (via M2)
- computer component design (via Intel)

Improving the understanding of the SO interaction, will inform the improvement and potentially, the development of new industrial techniques. In particular the SO interaction is key in

- magnetocrystaline anisotropy, the key process in the manufacture of ferromagnetic materials
- giant magnetoresistance, the key process in the operation of hard-drive read-heads

Both the PDRA and PhD student will receive high-end technical training relevant to academia and industry, both in HPC techniques and fundamental science. Our record in preparing researchers for positions outside of academia is evidenced by the current high-level positions held by former CTAMOP members: Michael Lysaght at the Irish Centre for High-End Computing and Laura Moore at SAP.