High-performance computing and its applications to atomic structure physics [thesis]

Emily Kahl
2021
Modern atomic physics is increasingly dependent on the results of high-precision calculations to guide experiments and applications, especially in complex atoms with dense spectra. Many cutting-edge applications and experiments use atoms with open-shell electronic structure and strong configuration mixing, which require extremely large numerical bases to treat with any level of accuracy. At the same time, supercomputing clusters have seen huge increases in computational power, driven by
more » ... ngly large-scale parallelism across many distributed compute nodes. Consequently, modern atomic structure code must be designed to fully utilise massively-parallel computing resources if they are to keep up with the increasing demands of experimental studies.In this thesis, I present the results of work to modernise the AMBiT atomic structure software, which implements the configuration interaction with many-body perturbation theory (CI+MBPT) method, to take advantage of modern supercomputers. I present a detailed outline of the software engineering processes in converting AMBiT from an MPI-only model of parallelism to a hybrid MPI+OpenMP model, as well as the performance gains resulting from doing so. I show that the increased parallelism allows us to explore numerical saturation of the CI+MBPT method in open-shell atoms for the first time ever --- an investigation would not have been possible without the increased performance capabilities of modern supercomputers.I have applied the new AMBiT to calculations of atomic systems with a variety of electronic structures. Calculations of the highly-charged ions Sn7+-Sn10+, which are of experimental interest for their applications in extreme ultraviolet photolithography for semiconductor fabrication, show that AMBiT is highly efficient for ions with open d-shells. We achieve very close agreement with experimental spectra: CI+MBPT calculations differ from experiments by an average error of less than 1%. Additionally, calculations for two- and three-valent Lr+ and Lr demonstrate t [...]
doi:10.26190/unsworks/22401 fatcat:dou4xewwpjfr7g3p52ocgjlzk4