Electronic stopping power in liquid water for protons and \ensuremath{\alpha} particles from first principles

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Electronic stopping power in liquid water for protons and α particles from first principles

Kyle G. Reeves, Yi Yao, and Yosuke Kanai

Phys. Rev. B 94, 041108(R) – Published 14 July 2016

Abstract

Atomistic calculations of the electronic stopping power in liquid water for protons and α particles from first principles are demonstrated without relying on linear response theory. The computational approach is based on nonequilibrium simulation of the electronic response using real-time time-dependent density functional theory. By quantifying the velocity dependence of the steady-state charge of the projectile proton and α particle from nonequilibrium electron densities, we examine the extent to which linear response theory is applicable. We further assess the influence of the exchange-correlation approximation in real-time time-dependent density functional theory on the stopping power with range-separated and regular hybrid functionals with exact exchange.

Received 8 April 2016
Revised 17 June 2016

DOI:https://doi.org/10.1103/PhysRevB.94.041108

Physics Subject Headings (PhySH)

Atomic & molecular collisions

Liquids

Ab initio calculations Electronic structure Time-dependent DFT

General PhysicsAtomic, Molecular & Optical

Authors & Affiliations

Kyle G. Reeves, Yi Yao, and Yosuke Kanai^*

Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599, USA

^*Corresponding author: ykanai@unc.edu

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Vol. 94, Iss. 4 — 15 July 2016

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Figure 1
Electronic stopping power curves for a proton in liquid water. Two widely used empirical models, PSTAR [30] (black) and SRIM [31] (green), are shown for comparison. Experimental data based on work by Sz09 [34] and Sz10 [38] are shown as blue squares and purple diamonds, respectively. Our real-time TDDFT results are shown as the red line, and the error bars represent standard deviations for the path distribution.
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Figure 2
Analytical models of electronic stopping power and our real-time TDDFT results for a proton in liquid water. Analytical model using various model dielectric functions by Garcia-Molina [32] (cyan), Penn (blue), Ritchie (purple), Ashley (orange), and Emfietzoglou (green) are shown for comparison [2]. Bethe theory (black) is also shown with the mean excitation energy of $I = 75 eV$ as recommended by the International Commission on Radiation Units and Measurement [35]. Our real-time TDDFT results are shown as the red line, and the error bars represent standard deviations for the path distribution.
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Figure 3
Stopping power curves for a $α$ particle in liquid water. Two widely used empirical models, SRIM [31] (green line) and ASTAR [30] (black line), are shown for comparison to our real-time TDDFT results (red line). Experimental data for stopping power curves Ak80a (magenta circles, Ref. [36]), Pl78 (blue diamond, Refs. [34, 37, 38]), Hq85 (yellow squares, Ref. [39]), and Tw81 (purple triangles, Ref. [40]) are shown.
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Figure 4
Mean steady-state charge ( $\bar{q}$ ) for a proton (left) and an $α$ particle (right) in liquid water as a function of the projectile ion velocity. Error bars represent the standard deviations of the distribution of the instantaneous charge state, which is calculated using the Voronoi partitioning in the simulation (see text). The empirical model for the projectile charge state by Schiwietz and Grande is shown by the dashed line [33].
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Figure 5
Velocity-dependent ratios between protons and α particles for calculated stopping power and projectile ion charge state in liquid water. The ratio of the calculated electronic stopping power curves is shown as green diamonds. The ratio of the effective charge on each projectile is plotted as purple diamonds. The dashed line represents the stopping power ratio of 2, which is expected from linear response theory when assuming fully ionized charges.
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Figure 6
Normalized Gaussian distributions for the probability of observing a projectile proton with an instantaneous charge state, $q$ , in liquid water. Proton velocities of $v = 0.89 a . u .$ (left), $v = 1.9 a . u .$ (center), and $v = 6.27 a . u .$ (right) were simulated using three different exchange-correlation functionals: PBE (black), PBE0 (blue), and LC-BLYP (red).
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Physical Review B

covering condensed matter and materials physics

Electronic stopping power in liquid water for protons and α particles from first principles

Kyle G. Reeves, Yi Yao, and Yosuke Kanai

Phys. Rev. B 94, 041108(R) – Published 14 July 2016

Abstract

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Physical Review B

covering condensed matter and materials physics

Electronic stopping power in liquid water for protons and α particles from first principles

Kyle G. Reeves, Yi Yao, and Yosuke Kanai

Phys. Rev. B 94, 041108(R) – Published 14 July 2016

Abstract

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Authors & Affiliations

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