Yosuke Kanai of the University of North Carolina at Chapel Hill is supported by an award from the Chemical Theory, Models and Computational Methods program for computational work related to proton beam cancer therapy. Proton beam cancer therapies work by targeting cancer cells with high-energy protons. These protons damage the cancer cells by breaking the double strands of their DNA. In recent years, other particles, such as alpha-particles and carbon-ions, have been considered as alternatives to protons for cancer therapies. The energetic protons or other particles transfer their energy to the water and DNA by exciting their electrons. There is a strong need for a better understanding of the energy transfer process and electronic excitation process. Using massively parallel computers, Kanai and his research group develop and apply computational methods for simulating the energy transfer and electronic excitation process. Both graduate students and undergraduate students participate in this research.
A new large-scale, real-time, time-dependent density functional theory (TDDFT) method is employed to study electronic excitation dynamics in liquid water and solvated DNA under proton, alpha-particle and carbon-ion irradiation. The energy transfer from the high-energy ions depends significantly on the particle velocity. The perturbing electric field from the energetic ion is highly heterogeneous at the molecular scale. Using the real-time TDDFT method, the excitation process is investigated in detail as a function of the ion velocity and type (protons, alpha-particles, and carbon-ions). The energy transfer rate from the ions to electronic excitations in liquid water is determined from non-equilibrium simulations, and a microscopic understanding of the excitation dynamics in liquid water and solvated DNA is developed. Improving scalability of real-time TDDFT code on massively parallel computers and the exchange-correlation approximation for describing the dynamical energy transfer process are two important aspects of this investigation. Dr. Kanai also develops novel teaching computational tools for teaching time-dependent quantum mechanics in advanced chemistry courses.
