Excitation energy and pair correlation function of trions near an LiF surface

Abstract

We investigate the excitation spectrum of a singly charged LiF surface using an embedded cluster approach. The spectrum is determined by multiconfiguration self-consistent field calculations. We find stable trionic states, i.e., quasimolecular states of a three-quasiparticle complex consisting of two holes and one electron interacting through the Coulomb potential. The excitation energy of the lowest trionic state is approximately 12.1 eV. The mean hole-hole spacing is about 7.6 a.u. ͑or 4 Å͒. Our results confirm the interpretation of experiments ͓P. Roncin et al., Phys. Rev. Lett. 89, 043201 ͑2002͔͒ where trion excitation was suggested as effective energy-loss channel during the neutralization of Ne + ions at an LiF surface.

Trions in bulk LiF and at the LiF(001) surface

“…However, the experimental spectrum is very broad and we speculate that it might be a superposition with further states like the bulk trion observed in our study. The theoretical work of Solleder et al [6] on small LiF clusters has estimated minimal and maximal limits for the trion excitation energy of 10.5 to 12.1 eV, which are in reasonable agreement with our findings.…”

“…Until now the description of trions in LiF has been limited to the approximative multiconfiguration self-consistent field calculations of small clusters [6]. Furthermore, the usage of a Wannier-Mott model (i.e., employing k-dependent envelope functions) is questionable for LiF because excitations are strongly localized [7].…”