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).
