Correlated prediction of the photoelectron spectrum of polyethylene: Explanation of XPS and UPS measurements

The correlated quasiparticle energies for valence bands of polyethylene have been calculated, ab initio, employing many-body perturbation theory. Electron correlation effects for the bands vary from 1.5 to 5.4 eV. The MBPT(2) band energies accurately explain the measured photoelectron spectra (XPS, UPS) of polyethylene and resolve long-standing disagreements among these experiments. Density functional theory fails to provide agreement with experiment. This example demonstrates the critical role of correlated ab initio theory in obtaining accurate band structures for extended systems.