Grant: Discovery Grants Program - Individual

When an atom or a molecule is hit by an energetic ion or is exposed to a strong laser field it may release one or several of its electrons. In the case of a molecular target, this process of ionization may be followed by the break-up of the system into neutral and charged fragments which, similarly to the released electrons, may cause further ionization in surrounding matter. These processes are at the heart of the problem of radiation damage of biological tissue. Their quantitative understanding is the principal objective of this research program. Atoms and molecules follow the laws of quantum physics. When they are exposed to strong fields, either through collisional interactions or by laser illumination, the equations derived from those laws to describe their behaviour are so complex that exact solutions are not feasible. Models, advanced theoretical methods and numerical techniques are then required to make predictions on measurement outcomes or to produce numerical data that can be compared with available measurements to help understand the underlying physics and draw conclusions with regard to possible applications. The work described in this proposal is concerned with the development and execution of such models, methods and techniques. Two avenues of research will be pursued. On a fundamental level, we will use atomic collision problems as test beds for the further development of the so-called time-dependent density functional theory (TDDFT) approach, which is one of only a few theoretical methods available for describing collisional and laser-driven many-electron dynamics on a first-principles basis. We will implement a TDDFT scheme on a higher level of approximation than reported before and carry out numerical calculations for ion-atom collisions to help validate and improve the approach. We will also address an outstanding fundamental TDDFT problem related to the calculation of observable quantities. Our work will advance theory and produce data of interest to experimentalists in the field and to researchers in neighbouring disciplines who are, e.g., analyzing X-ray spectra of astrophysical objects or diagnosing high-temperature plasmas in the context of nuclear fusion experiments. On the more applied side we will study ion collisions from biologically relevant molecules, such as DNA/RNA building blocks, by elaborating on a simplified model description which we have proposed recently. Full first-principles calculations are not feasible for these complicated systems, yet reliable theoretical data would be important for an in-depth understanding of the problem of radiation damage of biological tissue. Our research is aimed at filling this void and producing such data. The results of our model calculations will benefit the field of radiobiology and, potentially, have an impact on clinical applications such as tumour therapy with positively-charged ions, thereby contributing to a more successful treatment of cancer.