Toward Routine Gauge-Including Projector Augmented-Wave Calculations for Metallic Systems: The Case of ScT₂Al (T = Ni, Pd, Pt, Cu, Ag, Au) Heusler Phases

Abstract

We use the gauge-including projector augmented-waves (GIPAW) method to report, for the first time, theoretical 27Al Knight shifts in metallic systems other than metallic Al. We consider metallic Al and a set of six intermetallic compounds, for which experimental chemical shifts were recently made available in the literature. The orbital and spin components of the chemical shielding tensors are computed from the same ground-state spin-polarized electronic structure, converged under the influence of a uniform external magnetic field. A linear response formalism is used to compute the orbital part, while the spin part is approximated by the linear relationship between the external field and the Fermi contact contribution to the induced magnetic hyperfine field at the nuclear position. Core spin-polarization effects are taken into account by means of a perturbative approach. Our results show that the GIPAW approach yields reasonably acceptable chemical shifts with affordable k-meshes in the irreducible Brillouin zone, enabling separation between contributions to metallic shifts from the electron orbital and from the electron spin susceptibilities.

On the use of atomistic simulations to aid bulk metallic glasses structural elucidation with solid-state NMR

“…Therefore, for a discussion of such experimental results, it is expected that the moderate precision and good accuracy achieved with the GIPAW method, demonstrated in ref. 20 , is enough. Moreover, since it does not make much sense to explore the anisotropy of the nuclear interactions in non-realistic structures, we have chosen ASs with a minimal influence of quadrupole effect and KS anisotropy, i.e., supercells not only with an affordable number of atoms, but also with rather symmetric structures.…”

“…Fortunately, they can be computed independently of each other and more details regarding theory and technicalities on their simulations can be found in ref. 20 .…”

“…In a recent report by one of us et al . 20 , this method was used successfully to quantify 27 Al chemical and Knight shifts (CS and KS) isotropic values for a series of intermetallic compounds with formulas Sc T 2 Al ( T = Ni, Pd, Pt, Cu, Ag, Au). We already stated that the computation of σ o and σ s components of the total shielding directly from the CMD derived large-scale structural models with 10000 atoms is not computationally feasible.…”

“…Actually, as well covered in ref. 20 , due to numerical convergence issues particularly for the σ o component, the GIPAW computations are already quite expensive for structures with more than 20 atoms. Notwithstanding these remarks, and besides the aforementioned premise that ssNMR is intrinsically a short-ranged limited characterization technique, we present another argument to justify the use of abstract systems (ASs) to perform our ab initio DFT simulations.…”

“…From the CMD derived structural models, conventional statistics allowed us to discover the main features of the SRO and MRO around the Al nuclei which are most likely to justify the experimental metallic shifts (CS plus KS). Then, following a recent use of the GIPAW method to quantify the CS and KS isotropic values in intermetallics compounds from first principles 20 , we apply it to a set of abstract systems (ASs) in the scope of ssNMR. From the results obtained, it was possible to revisit the correlations between metallic shifts and local/semi-local structure around Al sites proposed in the literature.…”