UNC-CH Physics and Astronomy Colloquium

Yosuke Kanai, University of North Carolina, Chapel Hill

“Electronic Stopping in Condensed Matter: Ab Initio Understanding of Electronic Excitation Dynamics under Proton Irradiation”

Transfer of the kinetic energy from a highly-energetic ion to electrons in condensed matter is described by the so-called electronic stopping. The projectile ions bear highly localized electric field that is quite heterogeneous at the atomistic scale, and massive electronic excitations are produced in the electronic stopping process. Understanding this phenomenon= in condensed matter systems under proton and other ion irradiation has implications in various modern technologies, ranging from nuclear fission/fusion reactors, to semiconductor devices for aerospace missions, to cancer therapy based on proton beam radiation. Electronic stopping has been long studied within linear response theory framework (e.g. Bethe theory), but recent advances in high-performance computers allow us to study the phenomena beyond such simplified treatment through the use of numerical simulations. In this talk, I will discuss how non-equilibrium dynamics simulations based on our recently-developed large-scale real-time time-dependent density functional theory enable us to study this electronic excitation process, using an important case of liquid water under proton irradiation as an example. In addition to determining the energy transfer rate (i.e. electronic stopping power), our work reveals several key features in the excitation dynamics at the mesoscopic and molecular levels for deciphering water radiolysis mechanism under proton irradiation.