Excitation Dynamics in Water under Proton Irradiation: Time-dependent Maximally-Localized Wannier Function Approach*

Proton irradiation of liquid water has many important medical applications, including proton beam therapy. However, understanding the quantum dynamical details of the electronic excitations of water induced by the energetic protons has long been intangible. Using the approach of propagating maximally localized Wannier functions (MLWFs) in real-time TDDFT, we study the molecular-level dynamics of the electronic excitations¹. These time-dependent MLWFs (TD-MLWFs) are localized in space, offering a convenient ‘chemical moiety’ picture of liquid water and allow for understanding of the electron dynamics in terms of bond centered and lone pair electrons of water molecules. The spatially-localized nature of the TD-MLWFs allows us to study the secondary electronic excitations from the electrons initially excited by the proton. The MLWF gauge also enables usage of the length-gauge to describe the homogeneous electric field to model photo-excitation, and analyze proton and photo- irradiation on equal footing.
¹J. Chem. Phys. 150, 194113 (2019)