Time dependent density functional investigation of the near-edge absorption spectra of V2O5

Abstract

We have performed Time Dependent Density Functional Theory (TDDFT) calculations employing a cluster model of the core excitation spectra of vanadium pentoxide, V(2)O(5). The excitation energies and dipole transition moments are determined for all the core edges, vanadium and oxygen K- and vanadium L-edges, treating them at the same level of accuracy. The agreement between the TDDFT theoretical spectra and the experimental data is rather good, particularly at the V and O K-edges. A quantitative reproduction of the fine pre-edge structures appears more difficult for the V L-edge. The comparison between the TDDFT results and the results obtained at the simpler one electron Kohn-Sham (KS) level indicates that the V and O K edges can be correctly described within a single particle approximation (KS), while the strong modification of the V L-edge structures from the KS to the TDDFT description emphasizes the importance of configuration mixing to treat the metal 2p excitations. The origin of the calculated pre-edge features is analyzed in detail with the help of the atom-projected density-of-states of the unoccupied levels. This analysis emphasizes the V 3d dominant character of the final states in the conduction band, probed by the V L-absorption. The strong octahedral distortion of the V(2)O(5) structure allows the mixing of the 3d state with the V 4p components, which are mapped by the oscillator strength in the V K-edge spectrum. The high intensity of the O 1s transitions reflects the presence of a significant O 2p component in the conduction band.

First-principles calculations of X-ray absorption spectra at the K-edge of 3d transition metals: an electronic structure analysis of the pre-edge

“…24 These approaches include time-dependent DFT (TD-DFT), GW calculations and the Bethe-Salpeter equation. TD-DFT calculations have been performed at the V K-edge of V 2 O 5 , 25 and at the Fe K-edge of a series of ten iron model complexes, giving a correct agreement with experiment in the pre-edge region. 26 The Bethe-Salpeter approach has been applied to the calculation of the Ti K pre-edge structure in rutile 27 and in SrTiO 3 .…”

L2,3 edge photoabsorption spectra of bulk V2O5: A two components relativistic time dependent density functional theory description with finite cluster model

“…About the physical origin of this splitting, at the moment only hypothesis can be formulated: apart from effects not explicitly included in the calculations, for example, a possible coupling of electronic and vibrational states, it could be ascribed to the limited cluster size employed, with only one layer of V atoms; a three layer structure would have assured a more correct description of a bulk situation, with the V excited atoms placed in the middle layer and completely surrounded by cluster atoms with a consequent minimization of surface effects, as pointed out in the non-relativistic results in Ref. 31. However, the comparison between the V 10 O 31 H 12 and V 30 O 93 H 36 clusters at non-relativistic level did not show any emerging spectral feature as a shoulder at the right side of the main peak, so if the absence of P5 feature in the calculation is caused by the limited size of the cluster, it is more likely attributable to long-range effects, whose description needs really big models containing several hundreds of atoms.…”

“…The strategy used to cut out the cluster from the bulk structure of V 2 O 5 is described in Ref. 31.…”

“…31,32 Within a layer, three non-equivalent oxygen atoms are present: (a) apical oxygen, commonly designated as vanadyl oxygen, bound by double bond to a V atom and pointing towards the direction perpendicular to the layer, (b) chain oxygen, bridging two vanadium atoms, and (c) bridge oxygen, coordinated to three different vanadium atoms. The model cluster V 10 O 31 H 12 contains only one layer and it has been considered since the inter-layer interaction is of mainly electrostatic nature and therefore rather weak.…”

Vanadium Bisimide Bonding Investigated by X-ray Crystallography,51V and13C Nuclear Magnetic Resonance Spectroscopy, and V L3,2-Edge X-ray Absorption Near-Edge Structure Spectroscopy

“…Data were analyzed for agreement and possible absorption by use of XPREP. 105 An absorption correction based on comparison of redundant and equivalent reflections was applied by use of SADABS. 106 Structures were solved by direct methods with the aid of successive difference Fourier maps and were refined on F 2 by use of the SHELXTL 5.0 software package.…”