Core-level binding-energy shifts due to end effects in polymers: A Hartree-Fock Green's-function study.

Hartree-Fock Green's-function studies of end effects on the core-level structure of metallic and insulating quasi-one-dimensional model polymers reveal additional core peaks outside the bulk bands. In the metallic case, shifts to both lower (\ensuremath{\sim}-150 meV) and higher (\ensuremath{\sim}+50 meV) binding energies are observed, whereas in the insulating case, split-off peaks occur only at the lower-binding-energy side (\ensuremath{\sim}-150 meV). It is shown that a positive or negative net valence population alone does not determine the direction of the shift. The binding-energy changes are determined by a detailed balance between the energy loss due to a decrease in the electron-nuclear attraction and the energy gain due to a decrease in the electron-electron repulsion experienced by the core electrons of the end atoms. This can probably also explain why for some metal surfaces, shifts towards lower, and for others, shifts towards higher, binding energies are found. In the valence region of the investigated lithium chains, the ends do not produce localized end states.