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

摘要: Knowledge of the electronic stopping curve for swift ions, $S_e(v)$, particularly around Bragg peak, is important understanding radiation damage. Experimentally, however, determination such feature light ions very challenging, especially in disordered systems as liquid water and biological tissue. Recent developments real-time time-dependent density functional theory (rt-TDDFT) have enabled calculation $S_e(v)$ along nm-sized trajectories. However, it still a challenge to obtain meaningful statistically averaged that can be compared observations. In this work, taking advantage correlation between local structure probed by projectile distance from atoms target, we devise trajectory pre-sampling scheme select, geometrically, small set short trajectories accelerate convergence computed via rt-TDDFT. For protons water, first calculate reference probability distribution function (PDF) proton closest oxygen atom, $\phi_R(r_{p{\rightarrow}O})$, length similar those sampled experimentally. Then, are sequentially selected so accumulated PDF reproduces $\phi_R(r_{p{\rightarrow}O})$ increasingly high accuracy. Using these pre-sampled trajectories, demonstrate $S_e(v_p)$ converges whole velocity range with less than eight while other averaging methods using randomly uniformly distributed require approximately ten times computational effort. This allows us compare experimental data, assess widely used empirical tables based on Bragg's rule.