This project will establish a predictive computational framework for quantum-mechanical, first-principles modeling of dynamical response of electrons to charged-particle radiation in semiconductors and water/DNA. Quantum dynamics simulations will uncover detailed mechanisms that are central to a wide range of applications, from aerospace electronics to proton beam therapy.

A fast, charged particle entering a target material produces complicated effects on a range of length and time scales. At the atomistic level, these begin on atto- to femto-second (one-quintillionth to one-quadrillionth of a second) time scales. Existing models for calculating electronic stopping power (transfer of energy from a charged particle into an electronic system) lack predictive capability and atomistic details. At the same time, first-principles electron dynamics simulations are very computationally demanding.

The team’s implementation of Ehrenfest molecular dynamics into the Qbox/Qb@ll code, based on real-time time-dependent density functional theory, combines the quantum dynamics of electrons and the classical movement of ions for a quantitative understanding of these systems. The team focused its code development on strong scalability over many processors, allowing for accurate simulations of the dynamics of thousands of electrons on these ultrafast time scales.

On Mira, the team is modeling electronic stopping in three semiconductor materials with different band gaps, or degrees of electrical conductivity, and native defects. Preliminary studies have shown that both of these properties influence electronic stopping. They are also examining how highly energetic protons interact with DNA and water, as these protons can directly damage DNA or indirectly damage it through ionization of water. Detailed understanding of this interaction is of great importance for the semiconductor industry, for ensuring human health in space, and for advancing proton beam therapy for cancer treatment.