Combination of the TD-DFT and the pixel counting method for determining electron capture cross sections for protons impacting on organic molecules

Abstract

The electron capture by heavy charged particles is of interest in a wide range of physical applications. In radiation biophysics, electron capture cross sections (ECCS) is a key information for the implementation of Monte Carlo simulation codes. In this work, the time-dependent density functional theory (TD-DFT) has been used for the determination of ECCS for protons impacting on atoms with presence in organic compounds, in the 1–200 keV energy range. Later, these atomic cross sections were combined through the pixel counting method for determining corresponding cross section of small and large organic molecules and water, which is of primordial importance in radiation biophysics. The large organic molecules include DNA bases and a whole DNA base pair. Excellent results were obtained for the small molecules along the whole energy range. For DNA components, good results were found at high energies (100–200 keV). At lower energies, larger discrepancies were obtained when compared with other theoretical and experimental work. The possible causes for these discrepancies are deeply discussed. This work should support later works for developing a charge equalization method for classical molecular dynamics to describe fast proton collisions with organic materials.