  Chemical defects in polyethylene (PE) can deleteriously downgrade its
electrical properties and performance. Although these defects usually leave
spectroscopic signatures in terms of characteristic luminescence peaks, it is
nontrivial to make unambiguous assignments of the peaks to specific defect
types. In this work, we go beyond traditional density functional theory
calculations to determine defect-derived emission and absorption energies in
PE. In particular, we characterize PE defect levels in terms of thermodynamic
and adiabatic charge transition levels that involve total energy calculations
of neutral and charged defects. Calculations are performed at several levels of
theory including those involving (semi)local and hybrid electron
exchange-correlation functionals, and many-body perturbation theory. With these
critical elements, the calculated defect transition levels are in excellent
correspondence to observed luminescence spectra of PE, thus clarifying and
confirming the origins of the observed peaks. Based on this work, a
prescription with a reasonable computational expense is proposed to accurately
predict and assign spectroscopic signatures of defects in other organic
polymers as well.
