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

北卡罗来纳大学教堂山分校的金井裕介因与质子束癌症治疗相关的计算工作而获得化学理论、模型和计算方法计划颁发的奖项。质子束癌症疗法的工作原理是以高能质子靶向癌细胞。这些质子通过破坏癌细胞的DNA双链来破坏它们。近年来，其他粒子，如阿尔法粒子和碳离子，被认为是癌症治疗中质子的替代品。高能质子或其他粒子通过激发它们的电子将它们的能量传递给水和DNA。我们迫切需要更好地理解能量传递过程和电子激发过程。利用大规模并行计算机，金井和他的研究小组开发并应用计算方法来模拟能量转移和电子激发过程。采用一种新的大尺度、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。高能离子的能量传递很大程度上依赖于粒子速度。高能离子产生的微扰电场在分子尺度上是高度不均匀的。利用实时TDDFT方法，详细研究了激发过程随离子速度和离子类型(质子、α粒子和碳离子)的变化。通过非平衡模拟确定了液态水中离子到电子激发的能量传递速率，发展了对液态水和溶剂化DNA中激发动力学的微观理解。在大规模并行计算机上提高实时TDDFT代码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。金井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依赖时间的量子力学。

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.