UK R-matrix Atomic and Molecular Physics HPC Code Development Project (UK-RAMP)

Lead Research Organisation: Queen's University Belfast
Department Name: Sch of Mathematics and Physics

Abstract

New areas of Science are emerging for which multi-electron dynamics in atoms and molecules are crucial. One important example is the field of Atto-second Science where laser light and the electrons of matter interact on the atto-second time-scale making possible, for example, the shortest-ever pulses of VUV light. One atto-second is only one millionth-millionth-millionth of a second but electrons driven by strong laser light collide violently with others and move distances large compared to the size of an atom on the atto-second time-scale of several hundred atto-seconds. Another important example is the recent appreciation that ionizing radiation damages living animals and plants by bringing about strand breaks in the DNA molecule through a multi-electron interaction.Such newly emerging areas of Science involve large experimental teams in the UK and around the world who publish their research findings in top journals such as Nature and Science. Despite this, there does not yet exist anywhere in the world a set of computer codes capable of calculations of sufficient sophistication to be useful in conjunction with the laboratory experiment effort, in driving the Science forward. Such calculations demand the full power of present (and prospective) High Performance Computing - available through machines which presently can cost 100M and upwards.The purpose of the proposed research is to develop a suite of high-quality computer codes that will be widely used; will harness such high performance computing machines most effectively over many years; and will relate directly to areas of Science (brief descriptions of two such areas given above) where a detailed account of multi-electron dynamics in electrons and molecules is essential to driving the Science forward.
 
Description Through the funded research, we have developed new software to describe the ultra-fast dynamics of electrons within an atom. Recent laser technology has enabled experiment to influence the electronic motion on a timescale corresponding to orbit time of an electron around the nucleus. The computer codes developed enable us to investigate these processes computationally in an accurate fashion by taking the interactions between all electrons into account.

Through development of this code, we have made significant computational advances in atomic physics. We have combined the capability of basis-set techniques to describe multi-electron atoms with the computational efficiency of finite-difference techniques once an electron has moved away from the nucleus and the remaining electrons. This technique has been demonstrated to be extremely promising for efficient high-accuracy calculations, and is portable to other areas of computational science.

The codes have been specifically designed with high-performance computing facilities in mind. We have therefore explored new parallelisation schemes, in which the basis-set description is parallelised over symmetry first, and then distributed further
over MPI tasks within each symmetry. The finite-difference region has been separated into sectors associated with MPI tasks, and then
further parallelised using OpenMP threads. The resulting code has been demonstrated to efficiently exploit up to 3000 cores working simultaneously on a single problem.

The codes have been applied to a range of scientific problems of topical interest. We have been able to investigate photoionization time delays and have provided benchmark data for time delays in Ne. The time-dependent R-matrix codes have been applied to harmonic generation, where we have been able to demonstrate that the interplay between channels can be important in atoms, and that harmonic generation is not always associated with the lowest ionization threshold. Using the newly developed codes, we have been able to extend our description of harmonic generation into the highly challenging mid-IR regime, which is increasingly attracting experimental interest. We have furthermore demonstrated the accuracy of the final wavefunctions through the accurate determination of ejected-electron spectra for atoms in mid-IR fields. Recently, we have been able to
apply the codes to investigate the efficiency of harmonic generation from inner shells using ultra-short light pulses.

Most recently, we have developed a two-electron outer region approach for use within R-matrix theory, which provides new capability for the study of ultra-fast atomic dynamics. The two-electron outer region uses a finite difference description for two electrons. We have demonstrated the numerical stability of this new technique by applying the code to the study of double ionization processes, of importance at newly opened VUV and X-ray free-electron laser facilities.
Exploitation Route The prime aim of theoretical atomic physics is to provide understanding of basic atomic processes. These processes play a key role in the commissioning of VUV and X-ray free-electron laser facilities to demonstrate that these facilities perform as planned. Theoretical support is key, as validation of experiments on atoms in entirely new circumstances. Hence the findings are of prime use in the development of new laser technology.

The code development has proven to inspire planned code developments to understand ultra-fast dynamics in molecules. The demonstration that techniques work well for atoms will encourage molecular physics researchers to adapt their codes along similar
lines to extend the techniques to molecular systems. In the future, this may lead to a better understanding of charge-transfer processes in particular, a type of process critical in vision.

The computational techniques have proven to be very accurate indeed. The combination of basis-set techniques and finite-difference techniques works well, and may be taken forward by other computational scientists in their areas of research. The need for accuracy in the time-dependent codes has necessitated improvements in the accuracy of the underlying basic R-matrix codes, and researchers using these codes can therefore obtain more
accurate data on electron-scattering processes and photoionization processes of importance in all areas of plasma physics, including fusion science.
Sectors Aerospace, Defence and Marine,Digital/Communication/Information Technologies (including Software),Energy,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology
 
Description The most immediate non-academic impact is found in the training of young researchers in large-scale parallel computing. Researchers trained in these methods have, for example, become a Belfast-based industry leader in cloud computing research, and a Dublin-based leader of the Novel Technologies Activity and the Intel Parallel Computing Centre at the Irish Centre for High End Computing (ICHEC). The availability of high-quality graduates has led to significant inward investment by the financial-software industry in Belfast.
First Year Of Impact 2013
Sector Digital/Communication/Information Technologies (including Software)
Impact Types Economic
 
Description Software infrastructure
Amount £433,575 (GBP)
Funding ID EP/P022146/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 09/2017 
End 08/2019
 
Description Standard Research
Amount £376,329 (GBP)
Funding ID EP/P013953/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 05/2017 
End 04/2020
 
Description embedded computational science and engineering eCSE
Amount £63,007 (GBP)
Funding ID eCSE02-06 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Department ARCHER Service
Sector Academic/University
Country United Kingdom
Start 10/2014 
End 06/2015
 
Title R-matrix with time dependence code RMT 
Description The R-matrix including time dependence code combines the strengths of the existing time-dependent R-matrix codes and the HELIUM codes in a new time-dependent code for ultra-fast dynamics in atoms. It combines an R-matrix basis-set description in an inner region close to the nucleus with a finite-difference representation for an outgoing electron in an outer region. Compared to the previous time-dependent R-matrix code, it has greatly improved stability for the treatment of atomic systems in IR fields and allows parallelisation over many thousands of cores. 
Type Of Technology Software 
Year Produced 2013 
Impact The RMT code has been used for comparison with experiment to validate a new experimental technique for time-resolved four-wave mixing spectroscopy. 
 
Title RMT code for double ionization 
Description This particular application of the RMT codes has the capability to describe double ionization processes whereby two electrons can be described at large distances from the nucleus. This is a significant advance compared to the standard RMT code which can only account for one electron to move far away from the nucleus. 
Type Of Technology Software 
Year Produced 2015 
Impact None so far