R-matrix suites for multielectron attosecond dynamics in atoms and molecules irradiated by arbitrarily polarised light

In this project, we will develop new software for the accurate description of atoms and molecular systems in intense, ultra-short light fields with arbitrary polarisation. This involves generalising two world-leading suites of codes: The R-matrix with time-dependence codes (RMT) for ultra-fast atomic dynamics and the UKRmol+ suite for electron/positron scattering and photoionisation processes in molecules. By making these codes available to the wider community, in a form that can be easily used and efficiently run, we will help build the software infrastructure in the UK.

Significant development in laser technology over the last couple of decades has led to the birth of attosecond science: lasers are now available that can produce extremely short pulses (around 0.1 femtosecond or 10(-16) s in duration) to image and control the motion of electrons in atoms and molecules. This development has, for example, enabled scientists to 'see' how charge is transferred in a molecule after it is ionised, a process that has biological importance (for example, in photosynthesis).

Light can be treated as an electromagnetic wave; the direction in which the electric field oscillates defines the polarisation of the light. This polarisation, in turn, determines how the light interacts with matter. Until very recently intense, ultra-short light pulses were linearly polarised. However, it has recently become possible to generate laser pulses with different types of polarisation. New scientific research areas and new opportunities have become available via these latest technological developments. With control over the polarisation of light pulses, one can control the electron dynamics and even fine-tune it: In simple terms, using light pulses which oscillate in more than one-dimension gives an additional control parameter in experiments, and this is the underlying mechanism in so-called multidimensional spectroscopy. This field is becoming increasingly interesting, as experiments begin to probe the interface of the quantum and classical worlds.

In addition, light pulses with elliptical polarisation will enable the detailed study of electron dynamics in chiral molecules. (Chiral molecules are those that cannot be superimposed to their mirror images, like human hands). These molecules are immensely interesting: a lot of biologically important molecules, like the amino acids and sugars that are building blocks of living organisms are 'homochiral': only one variant is present in life (but never its mirror image).

New computer codes, which can handle general atomic and molecular systems in arbitrarily polarised light are needed to complement experimental advances, to assist in their theoretical interpretation and also to guide them. At present, the RMT codes can model atoms in a linearly polarised light field. Expanding them to treat the effect of arbitrarily polarised light is a substantial task: It requires lifting symmetry restrictions which have limited the size of previous calculations, and consequently a significant improvement in the codes' efficiency to account for the much larger-scale calculations will be necessary. In addition, we will massively expand the impact of the method by developing an equivalent method to treat molecules in a time-dependent fashion. The data needed to study the effect of the laser pulses on molecules will be generated by the UKRmol+ suite. This, in turn, requires the overhauling of these codes so they can produce sufficiently accurate input in an efficient way.

The computational development within this project will be strongly connected to the CCPQ community, which involves research groups across the UK developing scientific software for use in atomic and molecular physics and computational chemistry. Through CCPQ we will not only share the suites of codes, but also the expertise and software development skills gained.

The major impact of the project will be the provision of two software suites which will enable new computational science and support and guide experimental research exploiting state-of-the-art light technology. We will develop a community of users through tools on the CCPForge portal, where the codes will be made freely available to researchers. We will showcase the benefits and capabilities of the suites through presentation at scientific conferences and continued participation in national (CCPQ) and international training and collaboration networks. We will also provide training in the use of the suites through a dedicated training workshop.

Code developments within this project will be shared with other developers of R-matrix based software for atomic and molecular processes impacting, for example, on the diagnostics of plasmas and their contamination in nuclear fusion reactors. Better understanding of all processes occurring within a reactor will ultimately enable the development of such reactors for energy generation. The software will also be made available to researchers at STFC Daresbury Laboratory and the Irish Centre for High-End Computing for porting onto emerging compute technologies, with a view to inclusion in application benchmark suites.

The codes will impact on the study of processes involving sub-femtosecond electron dynamics, an area which has opened up with the advance of short-pulse light technology. This dynamics underpins photochemical processes of fundamental importance, including photosynthesis, vision and the function and manufacture of solar cells. The capability to treat light with arbitrary polarisation will enable better understanding of the chiral nature of asymmetric molecules. Accurate measurement techniques which probe this chirality are in demand because of the proliferation of chiral molecules in medical applications, and the potentially very dangerous use of apparently equivalent molecules of the wrong symmetry (e.g.Thalidomide).

The proposed developments will also impact on emerging laser technologies based on high harmonic generation (HHG), and on emerging measurement techniques such as multidimensional spectroscopy. These techniques rely on full spatial control over the electronic wavepackets, which can be achieved using circularly polarised or cross polarised light pulses. Our work will allow modelling of the full motion of the electron wavepacket, providing unparalleled insight into possible optimisations and applications of HHG and new measurement techniques.

The UKRmol+ suite is used worldwide to study electron and positron collisions with molecules. Developments will enable current users to tackle problems of applied interest (e.g. processes relevant to focused electron beam induced deposition and damage induced by ionisation radiation in the cell). In addition, since the new suite will enable efficient calculation of quantities required for photoionisation calculations, it will open up its use to a new community.

This suite will be taken up by Quantemol Ltd., who provide expert-system software for quantum mechanical problems of practical importance. Quantemol is currently involved with academic and industrial research in technological plasmas. Quantemol will adapt their products for use with the UKRmol+ suite, which will increase their customer base. The description of the interaction of molecules and light will furthermore allow new product development.

Building on the OU's long history of collaboration with the BBC, we will make a YouTube video explaining the research to a general audience, especially the connection to real-world applications like photosynthesis, vision, radiation damage and solar energy. We will also continue to contribute to the Northern Ireland Science Festival, through the annual exhibit of the School of Mathematics and Physics in the Ulster Museum (http://www.nisciencefestival.com/programme.php?c=maths_and_physics).