Examining real-time TDDFT non-equilibrium simulations for the calculation of electronic stopping power

TL;DR

This paper evaluates the accuracy of real-time TDDFT simulations in calculating electronic stopping power during ion irradiation, analyzing the impact of various approximations and proposing a correction scheme for core-electron effects.

Contribution

It provides a comprehensive analysis of the physical and numerical approximations in RT-TDDFT simulations for electronic stopping power in crystalline silicon and introduces a correction scheme for core-electron contributions.

Findings

Approximations significantly affect stopping power calculations.

Core-electron excitations are important at high proton velocities.

Proposed correction improves the accuracy of simulations.

Abstract

In ion irradiation processes, electronic stopping power describes the energy transfer rate from the irradiating ion to the target material's electrons. Due to the scarcity and significant uncertainties in experimental electronic stopping power data for materials beyond simple solids, there has been growing interest in the use of first-principles theory for calculating electronic stopping power. In recent years, advances in high-performance computing have opened the door to fully first-principles nonequilibrium simulations based on real-time time-dependent density functional theory (RT-TDDFT). While it has been demonstrated that the RT-TDDFT approach is capable of predicting electronic stopping power for a wide range of condensed matter systems, there has yet to be an exhaustive examination of the physical and numerical approximations involved and their effects on the calculated stopping power. We discuss the results of such a study for crystalline silicon with protons as irradiating ions. We examine the influences of key approximations in RT-TDDFT nonequilibrium simulations on the calculated electronic stopping power, including approximations related to basis sets, finite size effects, exchange-correlation approximation, pseudopotentials, and more. Finally, we propose a simple and efficient correction scheme to account for the contribution from core-electron excitations to the stopping power, as it was found to be significant for large proton velocities.