On the prediction of electronic stopping power from first principles
type: CreativeWork
description: The prediction of electronic stopping power in materials from first principles using real-time time-dependent density functional theory, as implemented in the SIESTA code, combines classical motion of the nuclei with evolution of the electronic wavefunctions according to the time-dependent Kohn-Sham equation. The wavefunctions are numerically integrated according to the Crank-Nicolson integrator algorithm. In this work a correction to the existing Crank-Nicolson algorithm was implemented in parallel, based on using the correct time-dependent Kohn-Sham equation involving the covariant derivative of the wavefunction for a moving basis, and was shown to reproduce expected experimental results including oscillations of the Kohn-Sham energy for a projectile starting to move from a stationary position, which were lacking with the original integrator. The new integrator also predicted the electronic stopping power for a proton in graphite in line with experimental results, at velocities between 0.1 a.u. and 10 a.u., when the original integrator had been demonstrated to be inaccurate at velocities above 1 a.u.. The accuracy, convergence with timestep, and parallelisation of the new integrator was examined using example simulations of a proton projectile in graphite, and two helium atoms. The new integrator is not strictly unitary, unlike the previous implementation, and therefore requires a smaller timestep for accuracy. The removal of the basis changing step, which dealt with the moving basis in the original integrator via Lowdin orthonormalisation, resulted in a significant increase in speed using the new integrator, as a result of the removal of the computationally expensive matrix inversion in the basis change. The implementation of this new integrator extends the velocity range over which electronic stopping power can be calculated using the SIESTA code in any material above 1 a.u.; this allows exploration of higher projectile energy ranges. The prediction of electroni…
abstract: The prediction of electronic stopping power in materials from first principles using real-time time-dependent density functional theory, as implemented in the SIESTA code, combines classical motion of the nuclei with evolution of the electronic wavefunctions according to the time-dependent Kohn-Sham equation. The wavefunctions are numerically integrated according to the Crank-Nicolson integrator algorithm. In this work a correction to the existing Crank-Nicolson algorithm was implemented in parallel, based on using the correct time-dependent Kohn-Sham equation involving the covariant derivative of the wavefunction for a moving basis, and was shown to reproduce expected experimental results including oscillations of the Kohn-Sham energy for a projectile starting to move from a stationary position, which were lacking with the original integrator. The new integrator also predicted the electronic stopping power for a proton in graphite in line with experimental results, at velocities between 0.1 a.u. and 10 a.u., when the original integrator had been demonstrated to be inaccurate at velocities above 1 a.u.. The accuracy, convergence with timestep, and parallelisation of the new integrator was examined using example simulations of a proton projectile in graphite, and two helium atoms. The new integrator is not strictly unitary, unlike the previous implementation, and therefore requires a smaller timestep for accuracy. The removal of the basis changing step, which dealt with the moving basis in the original integrator via Lowdin orthonormalisation, resulted in a significant increase in speed using the new integrator, as a result of the removal of the computationally expensive matrix inversion in the basis change. The implementation of this new integrator extends the velocity range over which electronic stopping power can be calculated using the SIESTA code in any material above 1 a.u.; this allows exploration of higher projectile energy ranges. The prediction of electroni…
author: Halliday, Jessica
language: eng
keywords: electronic stopping
license: https://www.rioxx.net/licenses/all-rights-reserved/
date published: 2021-09-30
date modified: 2026-07-22T22:23:57Z
provider: Cambridge University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Cambridge

PropertyValue
property ID: DOI
value: 10.17863/CAM.87410