Interpretation of photoelectron spectra inCun−clusters including thermal and final-state effects: The case ofCu7−

We introduce an approach to investigate thermal effects on the photoelectron spectra of small clusters. By combining first-principles molecular dynamics and a simplified scheme to account for final-state relaxation effects, we obtain averaged excitation spectra at finite temperature. We apply our approach to the case of ${\mathrm{Cu}}_7^{\mathrm{}\mathrm{-}}$, in which two isomers are found very close in energy at T=0 K. At T=400 K, the isomer of ${\mathit{D}}_{5\mathit{h}}$ symmetry transforms into one of ${\mathit{C}}_{3\mathit{v}}$ symmetry. This behavior is in accord with the observed photoelectron spectra in which the predominant features can be associated with the ${\mathit{C}}_{3\mathit{v}}$ isomer. The averaged spectrum at T=400 K for this isomer suggests that the splitting observed in the peak at lowest excitation energies is a thermal effect. © 1996 The American Physical Society.