Space charges and deep traps in polyethylene — Ab initio simulations of chemical impurities and defects

In the framework of Density Functional Theory (DFT), we calculate the electronic structure of an amorphous polyethylene (PE) structure including defects and impurities. In particular, we provide tables with trap levels for defects like carbonyl groups at different chain locations, various double and triple bonds, hydroxyl and vinyl groups, and for impurities relevant for insulation applications, like acetophenone, alpha-methylstyrene, cumene, cumyl-alcohol, and water. It turns out that conjugated double-bonds and carbonyl groups yields generally the deepest traps. Shallow traps are seen for single double bonds in the PE chain, hydroxyl groups, and water. Traps originating from water, vinyl or hydroxyl groups have depths similar to the band gap of the amorphous-crystalline interface phase of PE; thus, these later defects could at high enough concentration bridge the interface phases yielding a sub-band in the band gap of PE.