Controlling multi-region multi-layered parallelisation for R-matrix with time-dependence, double ionisation

To 'view' electrons in an atom or molecule, we must capture their motion on a time-scale comparable to their interactions. Ultrashort laser pulses can image and control electrons in motion. Free-electron laser facilities operating in VUV, XUV and X-ray regimes have opened up new approaches to investigate ultra-fast dynamics on femtosecond and sub-femtosecond timescales. The complex physics induced by high-energy laser pulses requires close interaction with accurate theory to interpret experimental findings.

R-matrix with time-dependence (RMT) is the world’s most sophisticated code for correlated laser-driven multielectron dynamics in atoms and molecules driven by arbitrarily polarised pulses, including relativistic effects in atomic systems. A major extension treats double-ionisation phenomena: two interacting electrons may be ejected from an atom simultaneously. This massively increases complexity and computational workload. Physical space divides into three regions. The first surrounds the nucleus, utilizing a basis expansion for fully correlated multi-electron effects. The single-ionisation and the double-ionisation regions, with respectively one and two electrons far from the nucleus, utilizefinite-difference grids.