First principles calculations of the structure and V L-edge X-ray absorption spectra of V2O5 using local pair natural orbital coupled cluster theory and spin–orbit coupled configuration interaction approaches

Abstract

A detailed study of the electronic and geometric structure of V2O5 and its X-ray spectroscopic properties is presented. Cluster models of increasing size were constructed in order to represent the surface and the bulk environment of V2O5. The models were terminated with hydrogen atoms at the edges or embedded in a Madelung field. The structure and interlayer binding energies were studied with dispersion-corrected local, hybrid and double hybrid density functional theory as well as the local pair natural orbital coupled cluster method (LPNO-CCSD). Convergence of the results with respect to cluster size was achieved by extending the model to up to 20 vanadium centers. The O K-edge and the V L2,3-edge NEXAFS spectra of V2O5 were calculated on the basis of the newly developed Restricted Open shell Configuration Interaction with Singles (DFT-ROCIS) method. In this study the applicability of the method is extended to the field of solid-state catalysis. For the first time excellent agreement between theoretically predicted and experimentally measured vanadium L-edge NEXAFS spectra of V2O5 was achieved. At the same time the agreement between experimental and theoretical oxygen K-edge spectra is also excellent. Importantly, the intensity distribution between the oxygen K-edge and vanadium L-edge spectra is correctly reproduced, thus indicating that the covalency of the metal-ligand bonds is correctly described by the calculations. The origin of the spectral features is discussed in terms of the electronic structure using both quasi-atomic jj coupling and molecular LS coupling schemes. The effects of the bulk environment driven by weak interlayer interactions were also studied, demonstrating that large clusters are important in order to correctly calculate core level absorption spectra in solids.

Intermediate coupling for core-level excited states: Consequences for X-Ray absorption spectroscopy

“…[12] and for the analysis of NEXAFS edges see, for example, Ref. [16,17]. However, there is strong evidence that the methods that we develop to analyze and interpret the spectra of the Fe 3+ cation can also be applied for the analysis of materials models that take the oxide environment into account.…”

“…This is especially true for treatments that start from non-relativistic solutions and then add spin-orbit interactions; see, for example, Refs. [16,17]. Our work is unique in that we use the presence of multiplets as a physical tool to understand the properties of the excited states rather than primarily as a mathematical tool to obtain wavefunctions for the excited states [9,16,17].…”

Separation of valence states in thin films with mixed V2O5 and V7O16 phases

“…All three sets of data clearly show typical spin-orbit splitting at the vanadium L-edge around 518 eV and 523 eV. They are attributed to the vanadium L3 and L2 XAS features, respectively [37]. Also, two clear peaks are present at 529.5 and 531.5 eV, rising from oxygen K-electron excitations to the π* and σ* bands, respectively [37].…”

“…They are attributed to the vanadium L3 and L2 XAS features, respectively [37]. Also, two clear peaks are present at 529.5 and 531.5 eV, rising from oxygen K-electron excitations to the π* and σ* bands, respectively [37]. These two peaks are caused by transitions from O 1s level to O 2p levels hybridized with the V t2g and V eg levels, respectively [37,38].…”

Accuracy of DLPNO–CCSD(T) Method for Noncovalent Bond Dissociation Enthalpies from Coinage Metal Cation Complexes

“…4 DLPNO-CCSD(T) accuracy has been assessed on either full CCSD(T) or experimental data for some systems of interest including non-convalent interactions, 32 enzymatic reactions, 42 organic reactions [42][43] transition metals promoted reactions, [44][45][46][47] conformational issues in transition metal structures, 44 and even extended to solid oxide crystals 48 and a small protein. 35 However, in the majority of the cases the DLPNO-CCSD(T) method was validated against experimental data on transition metals reactions in solvent, [44][45][46][47] and consequently the accuracy of the combined DLPNO-CCSD(T)/particular solvation model was assessed rather than DLPNO itself.…”