Efficient ab initio calculation of electronic stopping in disordered systems via geometry pre-sampling: Application to liquid water

Abstract

J. (2020). Efficient ab initio calculation of electronic stopping in disordered systems via geometry pre-sampling: Application to liquid water.

Bragg's Additivity Rule and Core and Bond model studied by real-time TDDFT electronic stopping simulations: the case of water vapor

“…Since the electronic stopping power is very sensitive to the electronic density, its value depends quite significantly on the specific trajectory of the projectile (Sigmund, 2014;Correa, 2018;Dorado and Flores, 1993;Pruneda et al, 2007;Yao et al, 2019;Gu et al, 2020). In order to obtain a meaningful statistically averaged ( ) that can be compared to experimental data, it is necessary to run many short trajectories.…”

“…In order to obtain a meaningful statistically averaged ( ) that can be compared to experimental data, it is necessary to run many short trajectories. For targets in condensed phases and randomly selected trajectories, the number of trajectories is on the order of 100 (Yao et al, 2019;Gu et al, 2020). For the gaseous targets studied in this work, it can be expected that more trajectories of similar length are required to achieve an accurate ensemble average of , as the electronic density in gaseous targets is distributed more sparsely in the simulation box.…”

“…To accelerate the convergence of the running average of , we used our ion trajectory pre-sampling protocol based on a geometric criterion, to ensure that the probability distribution functions (PDFs) of the distance from the ion to the closest atoms, ( → ) (where is O or H in this work), accumulated over the selected trajectories, are close enough to the reference PDFs, ( → ), calculated with 50,000 randomly selected trajectories (Gu et al, 2020). To evaluate the similarity between ( → ), calculated for of a set of trajectories, and…”

“…For the stopping calculations we successfully applied our previously developed strategy for pre-sampling the projectile's trajectories (Gu et al, 2020), initially tested for liquid water, to the gas phase. Such strategy allows us to select a few short ion trajectories for which the averaged value of calculated by rt-TDDFT reproduces to an excellent extent the variety of different geometrical conditions of the encounters between projectile and target atoms realised in experiments (Gu et al, 2020), thus providing information beyond the "connectivity and conformation" perspective of the CAB approximation.…”

“…For the stopping calculations we successfully applied our previously developed strategy for pre-sampling the projectile's trajectories (Gu et al, 2020), initially tested for liquid water, to the gas phase. Such strategy allows us to select a few short ion trajectories for which the averaged value of calculated by rt-TDDFT reproduces to an excellent extent the variety of different geometrical conditions of the encounters between projectile and target atoms realised in experiments (Gu et al, 2020), thus providing information beyond the "connectivity and conformation" perspective of the CAB approximation. We chose to focus this study on water vapor, as the available experimental data has been, for a long time, the basis for studying energy deposition in liquid water by some first-generation track structure codes (Kyriakou et al, 2017), and it is still the case for state-of-the-art codes such as the recent TILDA-V (Alcocer-Ávila et al, 2019), KURBUC (Nikjoo et al, 2016) and the proton-induced low energy excitations/ionization in Geant4-DNA (Villagrasa et al, 2011;Miller and Green, 1973;Rudd et al, 1992).…”