Self-trapping of single and paired electrons in Ge ₂Se ₃

We report the theoretical prediction of single and paired electron self-trapping in Ge ₂Se ₃. In finite atomic cluster, density functional calculations, we show that excess single electrons in Ge ₂Se ₃ are strongly localized around single germanium dimers. We also find that two electrons prefer to trap around the same germanium dimer, rupturing a neighboring GeSe bond. Localization is less robust in periodic, density functional calculations. While paired electron self-trapping is present, as shown by wavefunction localization around a distorted GeGe dimer, single-electron trapping is not. This discrepancy appears to depend only on the boundary conditions and not on the exchangecorrelation potential or basis set. For single- and paired-electron trapping, we report the adiabatic barriers to motion and we estimate hopping rates and freeze-in temperatures. For the single trapped electron, we also predict the ⁷³Ge and ⁷⁷Se hyperfine coupling constants.