Core-level shifts in fcc random alloys: A first-principles approach

Abstract

First-principles theoretical calculations of the core-level binding-energy shift ͑CLS͒ for eight binary facecentered-cubic ͑fcc͒ disordered alloys, CuPd, AgPd, CuNi, NiPd, CuAu, PdAu, CuPt, and NiPt, are carried out within density-functional theory ͑DFT͒ using the coherent potential approximation. The shifts of the Cu and Ni 2p 3/2 , Ag and Pd 3d 5/2 , and Pt and Au 4f 7/2 core levels are calculated according to the complete screening picture, which includes both initial-state ͑core-electron energy eigenvalue͒ and final-state ͑core-hole screening͒ effects in the same scheme. The results are compared with available experimental data, and the agreement is shown to be good. The CLSs are analyzed in terms of initial-and final-state effects. We also compare the complete screening picture with the CLS obtained by the transition-state method, and find very good agreement between these two alternative approaches for the calculations within the DFT. In addition the sensitivity of the CLS to relativistic and magnetic effects is studied.

First principle calculations of core-level binding energy and Auger kinetic energy shifts in metallic solids

“…(7)] or two points, while the selection of three gives results very similar to the use of even further points. In a comparison between the transition state method and complete screening picture for the CLS in disordered alloys, it was found that the two computation schemes in most cases closely follow each other, however not with identical results [18].…”

“…Notice that while in principle Janak's theorem is only valid for the highest occupied electron, it has however also been successfully applied to core states [18,[37][38][39]. In the practical calculations, a fractional electron is promoted to the valence band leaving a fractional core-hole, ensuring charge neutrality and a full screening in similarity with the complete screening picture.…”

“…(2) [60]. In the demonstrations of the different shifts as average properties of volume and composition over substitutionally disordered fcc AgPd alloys in this work, the methodology is the same as in [18], however using LDA in all computational steps. The theoretical equilibrium volumes of pure metal Ag and Pd here correspond to S Ag W S = 2.91 a.u.…”

“…The CLS can then be readily calculated from the differences in the so-called generalized thermodynamic chemical potentials [16], which in turn are determined from total energies of the systems -where core electrons on the ionized atoms are promoted to the valence band, while the remaining electrons relax as they screen the core hole. First principles calculations within the complete screening picture have been successfully used in many different studies, ranging from the bulk core-level shift in disordered alloys [16][17][18], the disorder broadening of the spectral core-line in random phase alloys [19,20], surface core-level shifts [21][22][23], structural characterizations in different materials [24][25][26][27], and Auger kinetic energy shifts [28]. It was found that the transition state method, which also accounts for both initial and final state effects within a single framework without the necessity to separate them, though using one-electron eigenstates rather than total energies, gives similar results in several disordered alloys [18,29].…”

Near Ambient Pressure XPS Investigation of CO Oxidation Over Pd3Au(100)

“…The Au 4f7/2 core level (not shown) is also 137 shifted towards lower BE by ~0.6 eV for Pd3Au relative to pure Au. A discussion of the core level 138 shifts in the PdAu-alloy is beyond the scope of the present work, but has been previously been7 addressed by Olovsson et al [54]. Since the surface oxide incorporates Pd atoms only, the √5 oxide 140 peak positions are similar for Pd(100), Pd3Au(100) and Pd75Ag25(100).…”