First-Principles Simulation of Electronic Excitation Dynamics in Water and DNA under Proton Irradiation

位于查佩尔山的北卡罗来纳州大学的Yosuke Kanai获得了化学理论、模型和计算方法项目的一个奖项的支持，该项目的计算工作与质子束癌症治疗有关。质子束癌症疗法通过用高能质子靶向癌细胞来起作用。 这些质子通过破坏癌细胞DNA的双链来破坏癌细胞。 近年来，其他粒子，如α粒子和碳离子，已被认为是质子治疗癌症的替代品。 高能质子或其他粒子通过激发它们的电子将它们的能量转移到水和DNA。 有一个强烈的需要，以更好地了解能量传递过程和电子激发过程。 金井和他的研究小组使用大规模并行计算机开发和应用计算方法来模拟能量转移和电子激发过程。 本研究以研究生和本科生为研究对象，采用一种新的大规模、实时、含时密度泛函理论（TDDFT）方法，研究了质子、α粒子和碳离子辐照下液态水和溶剂化DNA中的电子激发动力学.高能离子的能量转移主要取决于粒子的速度。 高能离子的扰动电场在分子尺度上是高度不均匀的。使用实时TDDFT方法，详细研究了激发过程作为离子速度和类型（质子，α粒子和碳离子）的函数。从离子到液态水中的电子激发的能量转移速率是从非平衡模拟确定的，并且开发了对液态水和溶剂化DNA中的激发动力学的微观理解。提高实时TDDFT代码在大规模并行计算机上的可扩展性和描述动态能量传递过程的交换相关近似是本研究的两个重要方面。Kanai博士还开发了新的教学计算工具，用于在高级化学课程中教授时间相关量子力学。

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.