Near-Quantitative Predictions of the First-Shell Coordination Structure of Hydrated First-Row Transition Metal Ions Using K-Edge X-ray Absorption Near-Edge Spectroscopy

G0W0 Ionization Potentials of First-Row Transition Metal Aqua Ions

We report computations of the vertical ionization potentials within the GW approximation of the near-complete series of first-row transition metal (V-Cu) aqua ions in their most common oxidation states, i.e., V3+, Cr3+, Cr2+, Mn2+, Fe3+, Fe2+, Co2+, Ni2+, and Cu2+. The d-orbital occupancy of these systems spans a broad range from d2 to d9. All of the structures were first optimized at the density functional theory level using a large cluster of explicit water molecules that are embedded in a continuum solvation model. Vertical ionization potentials were computed with the one-shot G0W0 approach on a range of transition metal ion clusters (6, 18, 40, and 60 explicit water molecules), wherein the convergence with respect to the basis set size was evaluated using the systems with 40 water molecules. We assess the results using three different density functional approximations as starting points for the vertical ionization potential calculations, namely, G0W0@PBE, G0W0@PBE0, and G0W0@r2SCAN. While the predicted ground-state structures are similar to all three exchange-correlation functionals, the vertical ionization potentials were in closer agreement with experiment when using the G0W0@PBE0 and G0W0@r2SCAN approaches, with the r2SCAN-based calculations being significantly less expensive. Computed bond distances and vertical ionization potentials for all structures are in good agreement with available experimental data.

A Combined Wave Function and Density Functional Approach for K-Edge X-ray Absorption Near-Edge Spectroscopy: A Case Study of Hydrated First-Row Transition Metal Ions

The prediction of X-ray absorption spectra (XAS) of transition metal complexes has important and broad application areas in chemistry and biology. In this letter, we have investigated the predictive ability of multiconfiguration pair-density functional theory (MC-PDFT) for X-ray absorption spectra by calculating the metal K pre-edge features of aquated 3d transition metal ions in common oxidation states. MC-PDFT results were compared with experimentally measured spectra as well as analyzed against results from restricted active-space second-order perturbation theory (RASPT2) and time-dependent density functional theory (TDDFT). As expected, TDDFT performs well for excited states that can be accurately represented by singly excited configurations but fails for excited states where higher order excitations become important. On the other hand, both RASPT2 and MC-PDFT provide quantitatively accurate results for all excited states irrespective of their character. While core-level spectroscopy with RASPT2 is accurate, it is computationally expensive. Our results show that MC-PDFT performs equally well with significantly lower computational cost and is an encouraging alternate approach for X-ray spectroscopies.

Solution-Phase Synthesis of Vanadium Intercalated 1T'-WS2 with Tunable Electronic Properties

Metal ion intercalation into Group VI transition metal dichalcogenides enables control over their carrier transport properties. In this work, we demonstrate a low-temperature, solution-phase synthetic method to intercalate cationic vanadium complexes into bulk WS₂. Vanadium intercalation expands the interlayer spacing from 6.2 to 14.2 Å and stabilizes the 1T' phase of WS₂. Kelvin-probe force microscopy measurements indicate that vanadium binding in the van der Waals gap causes an increase in the Fermi level of 1T'-WS₂ by 80 meV due to hybridization of vanadium 3d orbitals with the conduction band of the TMD. As a result, the carrier type switches from p-type to n-type, and carrier mobility increases by an order of magnitude relative to the Li-intercalated precursor. Both the conductivity and thermal activation barrier for carrier transport are readily tuned by varying the concentration of VCl₃ during the cation-exchange reaction.

On the choice of reference orbitals for linear-response calculations of solution-phase K-edge X-ray absorption spectra

X-ray absorption spectra of liquids calculated with linear-response theories like TDDFT and CIS are dramatically improved with core-ion reference orbitals.