Calculation of C $1s$ core-level shifts in poly(ethylene terephthalate) and comparison with x-ray photoelectron spectroscopy

Using a first-principle approach, we investigate the C $1s$ core-level shifts of poly(ethylene terephthalate). The geometrical structure of the polymer is first fully relaxed, then the C $1s$ core-level shifts are obtained using an approach that includes core-hole relaxation. We compute shifts without geometry relaxation of the excited system, as well as with this relaxation, and find that one of the relative core-level shifts is affected by as much as 0.7 eV by this choice. We compare our ab initio core-level shifts with experimental x-ray photoelectron spectroscopy measurements.