Single-particle excitation of core states in epitaxial silicene

TL;DR

This study reexamines silicene's core-level XPS spectra and employs advanced $ ext{Δ}$SCF calculations to accurately determine single-particle excitation energies, resolving previous discrepancies and confirming DFT's effectiveness in surface electron interactions.

Contribution

It introduces a refined analysis of XPS spectra and applies a sophisticated $ ext{Δ}$SCF approach to accurately compute core-level excitation energies in silicene.

Findings

Theoretical core-level binding energies agree well with experimental XPS data.

Reanalysis of XPS spectra clarifies the sequence of Si 2p orbitals.

The study confirms DFT's capability to describe many-body electron interactions at surfaces.

Abstract

Recent studies of core-level X-ray photoelectron spectroscopy (XPS) spectra of silicene on ZrB$_2$(0001) were found to be inconsistent with the density of states (DOS) of a planar-like structure that has been proposed as the ground state by density functional theory (DFT). To resolve the discrepancy, a reexamination of the XPS spectra and direct theoretical access of accurate single-particle excitation energies are desired. By analyzing the XPS data using symmetric Voigt functions, different binding energies and its sequence of Si $2p$ orbitals can be assigned from previously reported ones where asymmetric pseudo-Voigt functions are adopted. Theoretically, we have adopted an approach developed very recently, which follows the sophisticated $\Delta$ self-consistent field ($\Delta$SCF) methods, to study the single-particle excitation of core states. In the calculations, each single-particle energy and the renormalized core-hole charge density are calculated straightforwardly via two SCF calculations. By comparing the results, the theoretical core-level absolute binding energies including the splitting due to spin-orbit coupling are in good agreement with the observed high-resolution XPS spectra. The good agreement not only resolves the puzzling discrepancy between experiment and theory (DOS) but also advocates the success of DFT in describing many-body interactions of electrons at the surface.