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Enabling Smart Computations to study space RADiation effects

Periodic Reporting for period 2 - ESC2RAD (Enabling Smart Computations to study space RADiation effects)

Reporting period: 2019-05-01 to 2021-08-31

The study of the impact of Space radiation, such as Galactic Cosmic Rays (GCRs) and Solar Energetic Particles (SEPs), on both biological matter as proxy for astronauts and component materials for a Space mission, is of fundamental importance for predicting the health risks incurred in Space and for estimating the lifetime of the mission.
The main objective of this project was to model the effects induced by the passage of relevant particles for Space mission scenarios (both primary ions and secondary electrons) in both biological matter (water, amino acids, DNA) and spacecraft solar cells, via first-principles approaches, namely Time Dependent Density Functional Theory (TDDFT) and ab initio Molecular Dynamics (AIMD). For biological matter, the electronic stopping, the excitation patterns at nanometer scale for proton impact on biological molecules, and the Energy Loss Function (ELF), Inelastic Mean Free Path (IMFP) and total/differential inelastic electron scattering cross sections in water to be given as direct input to Monte Carlo (MC) track structure codes have been investigated. For the solar cells, currently used triple-junction solar cells and hybrid organic-inorganic perovskite (HOIP) solar cells have been investigated, studying the accuracy of electronic stopping from TDDFT in multielement compounds, the dynamic nature of key quantities entering the Non Ionizing Energy Loss (NIEL) formula, the defects induced by realistic non-adiabatic collisional cascades, formulating new physically meaningful descriptors that relate the stability with the chemical bonding via compressed sensing/symbolic regression and by studying the NIEL in both HOIP and tandem solar cells. Spectra from trapped radiation, SEPs and GCRs have also been provided for a LEO, beyond LEO mission and a stay on Mars, later transporting them to and through the targets relevant for this project via MC particle transport.
For biological damage, we have developed a smart trajectory sampling scheme for making real time (rt) TDDFT calculations of the electronic stopping feasible in in disordered targets such as water and biomolecules in general (B. Gu et al, J. Chem. Phys. 153, 034113 (2020)), reducing the computational cost x10. The new sampling strategy has shown to perform efficiently also for amino acids and DNA. The study of the contribution to stopping from different chemical bonds for proton impacting on water molecules at the Bragg peak has allowed us to investigate potential improvements of the Bragg's additivity rule and of the Core and Bonding approach used in SRIM, whose low energy data are actually inherited by the internationally recommended ICRU datasets (B. Gu et al, to appear on Radiation Physics and Chemistry).
The scaling assumption currently used in MC track structure codes for deriving the stopping of other ions from protons was also investigated and a new scaling factor is now under design (B. Gu et al, in preparation). The patterns of excitations in solvated DNA samples under proton impact at Bragg peak energy (D. Muñoz-Santiburcio et al, article in preparation) and the analysis of the electronic excitation distributions and of the depopulation of the target's molecular orbitals demonstrated the necessity to include some of their solvation shell/s.
The ELF, electronic stopping and IMFP for electrons in water were investigated via linear response TDDFT, comparing with results from Drude-like models of the ELF used in MC track structure codes; the extraction of ab-initio inelastic scattering cross sections for electrons in water from the ELF calculations, a necessary input for track structure codes, has also been accomplished (N. Koval et al, to appear on Royal Society Open Science). Also, the comparison between the electronic stopping obtained from linear response and rt-TDDFT for protons, electrons and muons allowed us to highlight the limitations of the linear response theory for dealing with electrons (N. Koval et al, in preparation).
A roadmap for the ab-initio chemical-physics community was developed, highlighting the current status in the description of the physical, pre-chemical and chemical steps of radiation damage in biological matter and the challenges ahead to connect to the MC track structure community.
For the radiation effects in solar cells, we have at first investigated the predictive power/performance of rt-TDDFT calculations of the electronic stopping for proton impact on multi-element compounds for triple junction solar cells, against datasets considered as reference in the literature (N. Koval et al., R. Soc. Open Sci. 7: 200925 (2020)). Then, we investigated the influence of electronic excitations on one of the key quantities in the NIEL model, the threshold displacement energy, via AIMD, demonstrating that the presence of electronic excitations clearly favors the formation of defects on GaAs, but a small mitigating effect also exists due to a more facile healing in some cases (D. Muñoz Santiburcio et al, in preparation). The study of non-adiabatic cascades, by informing MD calculations of the electronic excitations calculated from rt-TDDFT, revealed deviations from the commonly used Norgett-Robinson-Torrens model (J. Teunissen et al, in preparation; T. Jarrin et al, Phys, Rev. B 104, 195203 (2021)).
For new solar cells, the relationship between chemical composition and strong bonding interactions in HOIPs, in a large chemical space, has been analyzed by a combination of DFT and compressed sensing – symbolic regression techniques, in order to derive new descriptors that highlight the non covalent-bonding contributions that can partially suppress halide migration (J. Teunissen and F. Da Pieve, J. Phys. Chem. C 125, 45, 25316 (2021)).
MC particle transport calculations have been performed for each of the studies above in order to provide realistic spectra for a mission at LEO (trapped radiation), interplanetary travel (SEPs) and on Mars (F. Da Pieve et al., J. Geophys. Res.: Planets 126, e2020JE006488 (2021)) propagated through the stack of triple junction solar cells and of both HOIP-based solar cells and tandem solar cells (J. Teunissen et al, in preparation).
This project has opened the path towards a better integration/combination of first-principles condensed matter/chemical physics approaches with MC particle transport methods, in the track structure approach for biological damage and in order to correct results from condensed history MC calculations of the NIEL on functional materials. Possible synergistic studies have been highlighted in several presentations at conferences and in a recently submitted chapter of a book (F. Da Pieve et al., Fundamentals of Monte Carlo particle transport and synergies with quantum dynamics for applications in ion-irradiated materials in Space and radiobiology, chapter, book of Cost Action TUMIEE 17126).
The ESC2RAD project results have had and will continue to have an impact on 1) the improvement of the basic understanding of the interaction between radiation and matter, in both biological targets and spacecraft components; 2) the creation of a new interface community, between the ab-initio+classical MD researchers and the Monte Carlo track structure community; 3) the training of highly specialized researchers who now have a rich expertise in rt-TDDFT for irradiation phenomena; 4) the understanding of phenomena of importance also for ion-beam cancer therapy and materials in nuclear reactors.
proton trajectory on a DNA fragment surrounded by water molecules