First-Principles Estimation of Core Level Shifts for Hf, Ta, W, and Re

Abstract

A simple first-principles approach is used to estimate the core level shifts observed in X-ray photoelectron spectroscopy for the 4f electrons of Hf, Ta, W, and Re; these elements were selected because their 4f levels are relatively close to the Fermi energy. The approach is first tested by modeling the surface core level shifts of low-index surfaces of the four elemental metals, followed by its application to the well-studied material TaSe 2 in the commensurate charge density wave (CDW) phase, where agreement with experimental data is found to be good, showing that this approach can yield insights into modifications of the CDW. Finally, unterminated surface core level shifts in the hypothetical MXene Ta 3 C 2 are modeled, and the potential of XPS for the investigation of the surface termination of MXenes is demonstrated.

Exploring the Charge Density Wave Phase of1T−TaSe2: Mott or Charge-Transfer Gap?

“…4(b) shows that each atom type has a different electronic occupancy. By integrating the PDOS over the energy range spanning the highest Ta-dominant VB (from −1.3 eV to E F , see Supplemental Material E [27]), the relative electronic charges S i¼A;B;C are estimated: electrons accumulate towards the center of the star (S A ≃ S B ≃ 0.76), depleting the tips (S C ≃ 0.45) [52]. This effect, perfectly consistent with the CDW description, is inherently governed by the electronic band configuration in the charge-ordered phase.…”