In honour of N. Yngve Öhrn: Surveying proton cancer therapy reactions with Öhrn's electron nuclear dynamics method. Aqueous clusters radiolysis and DNA-base damage by proton collisions

Proton cancer therapy (PCT) utilises high-energy H⁺ projectiles to cure cancer. PCT healing arises from its DNA damage in cancerous cells, which is mostly inflicted by the products from PCT water radiolysis reactions. While clinically established, a complete microscopic understanding of PCT remains elusive. To help in the microscopic elucidation of PCT, Professor Öhrn's simplest-level electron nuclear dynamics (SLEND) method is herein applied to H⁺ + (H₂O)_3-4 and H⁺ + DNA-bases at E_Lab = 1.0 keV. These are two types of computationally feasible prototypes to study water radiolysis reactions and H⁺-induced DNA damage, respectively. SLEND is a time-dependent, variational, non-adiabatic and direct-dynamics method that adopts a nuclear classical-mechanics description and an electronic single-determinantal wavefunction. Additionally, our SLEND + effective-core-potential method is herein employed to simulate some computationally demanding PCT reactions. Due to these attributes, SLEND proves appropriate for the simulation of various types of PCT reactions accurately and feasibly. H⁺ + (H₂O)_3-4 simulations reveal two main processes: H⁺ projectile scattering and the simultaneous formation of H and OH fragments; the latter process is quantified through total integrals cross sections. H⁺ + DNA-base simulations reveal atoms and groups displacements, ring openings and base-to-proton electron transfers as predominant damage processes.