Electronic excitations: Ab initio calculations of electronic spectra and application to zirconia ZrO2, titania TiO2 and cuprous oxide Cu2O

Dash, L. K.; Bruneval, Fabien; Trinité, Virginie; Vast, Nathalie; Reining, Lucia

doi:10.1016/j.commatsci.2005.09.010

Cited by 21 publications

(7 citation statements)

References 44 publications

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“…Local-field effects lead thus to a shift to higher energy and a decrease in intensity for the Mo-N 2,3 edges as already observed for other semicore states. 38,42,62,65 Focusing now on the low-energy part of the spectrum (E<22 eV), LFE induce an increase of intensity in the region situated around 15-20 eV, thus improving the agreement between experimental and calculated spectra. It is worth noting that thanks to an analogous band to band analysis as that described in section V, we are able to show that this increase of intensity results from the influence of LFE on the transitions from the O-s states towards the t 2g manifold.…”

Section: B Direct Comparison Theory/veels Experimentsmentioning

confidence: 99%

Strong anisotropic influence of local-field effects on the dielectric response ofα-MoO3

et al. 2013

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Dielectric properties of α-MoO 3 are investigated by a combination of valence electron-energy loss spectroscopy and ab initio calculation at the random phase approximation level with the inclusion of local-field effects (LFE). A meticulous comparison between experimental and calculated spectra is performed in order to interpret calculated dielectric properties. The dielectric function of MoO 3 has been obtained along the three axes and the importance of LFE has been shown. In particular, taking into account LFE is shown to be essential to describe properly the intensity and position of the Mo-N 2,3 edges as well as the low energy part of the spectrum. A detailed study of the energy-loss function in connection with the dielectric response function also shows that the strong anisotropy of the energyloss function of α-MoO 3 is driven by an anisotropic influence of LFE. These LFE significantly dampen a large peak in ε 2 , but only along the [010] direction. Thanks to a detailed analysis at specific k-points of the orbitals involved in this transition, the origin of this peak has not only been evidenced but a connection between the inhomogeneity of the electron density and the anisotropic influence of local-field effects has also been established. More specifically, this anisotropy is governed by a strongly inhomogeneous spatial distribution of the empty states. This depletion of the empty states is localized around the terminal oxygens and accentuates the electron inhomogeneity.

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Section: B Direct Comparison Theory/veels Experimentsmentioning

confidence: 99%

Strong anisotropic influence of local-field effects on the dielectric response ofα-MoO3

et al. 2013

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“…Traditional first-principle methods employed for the theoretical study of copper oxides range from basic density functional theory (DFT) within the local-density approximation (LDA) [10], via parametrized approaches (Hubbard's + U approach [11]), to more sophisticated hybrid functionals (HSE06 [12], B3LYP [13], PBE0 [14]) and studies using Green's functions and the screened Coulomb interaction [15,16] (so-called GW : G 0 W 0 (LDA) [17], GW RPA [18], scGW RPA [18], GW LF + V d (GGA+U ) [19]). Basic DFT (using LDA and GGA) has failed to predict the electronic and magnetic structures of all three copper oxides, giving rise to metallic and non-magnetic CuO and Cu 4 O 3 , and a very low band gap for Cu 2 O (0.5 eV [10]). The main modeling issue with those CuO and Cu 4 O 3 calculations lies within the strong hybridization between copper d and oxygen p orbitals.…”

Section: Introductionmentioning

confidence: 99%

Density functional theory study explaining the underperformance of copper oxides as photovoltaic absorbers

2019

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Most photovoltaic absorbers are identified using the standard Shockley-Queisser selection principle which relies on optimal band-gap values. However, this criterion has been shown to be insufficient, as many materials with appropriate values still perform badly. Here, we have employed calculations based on the density functional theory to assess three copper oxides as potential photovoltaic materials: Cu 2 O, Cu 4 O 3 , and CuO. Despite their promising theoretical solar power conversion efficiency of over 20%, experimental values are found to be far lower. Theoretical evaluation of the electronic and optical properties reveals that certain transitions within the band structures are dipole forbidden, whereas the fundamental band gaps of Cu 4 O 3 and CuO are of indirect nature. These findings correlate to the weak and shifted absorption properties found experimentally, which underpin the inefficient light capture by copper oxides. Based on these results and an applied extended selection metric, we can explain why copper oxides are unable to reach the efficiencies previously proposed theoretically and why we need to revise their maximum conversion values.

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“…23,[39][40][41] Also, it had been shown that a-TiO 2 films are well suited for surface passivation in bioimplant applications due to their high stability and corrosion resistance in vitro. 42,43 While there is extended literature 13,[44][45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62] on structural, elastic, thermodynamic, and optical/dielectric properties obtained from numerical simulations of the three most common crystalline phases as well as their low index surfaces, [63][64][65][66][67][68][69][70] computational data on a-TiO 2 are rather limited due to the necessity of using extended unit cells for an approximate numerical reproduction of amorphicity. In contrast to crystalline modifications, amorphous material phases stand out by their loss of translational symmetry/long-range order.…”

Section: Introductionmentioning

confidence: 99%

Fingerprints of order and disorder in the electronic and optical properties of crystalline and amorphous TiO2

et al. 2012

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We have investigated the structural and electronic properties as well as the linear optical response of amorphous TiO 2 within density functional theory and a numerically efficient density functional based tight-binding approach as well as many-body perturbation theory. The disordered TiO 2 phase is modeled by molecular dynamics. The equivalence to experimentally characterized amorphous phases is demonstrated by atomic structure factors and radial pair-distribution functions. By density functional theory calculations, using both the semilocal Perdew-Burke-Ernzerhof functional and the nonlocal Heyd-Scuseria-Ernzerhof screened hybrid functional, the electronic energy gap is found to be larger than in the crystalline TiO 2 phases rutile and brookite but close to the anatase band gap. The quasiparticle energy gap of amorphous TiO 2 is determined to be 3.7 eV, while the optical gap is estimated to 3.5 eV. The disorder-induced formation of localized electronic states has been analyzed by the information entropy of the charge density distributions. The frequency-dependent optical constants, calculated from the complex dielectric function, have been determined in independent particle approximation. Besides similar absorption characteristics between the most common crystalline phases and amorphous TiO 2 , we find distinct differences in the optical spectra in the energy region between 5 eV and 8 eV. These differences can be assigned to the loss of symmetry in the local atomic structure of the disordered material. While the composition of the crystalline phases rutile, anatase, and brookite is well described by periodic arrangements of distorted TiO 6 octahedra building blocks, the amorphous phase is characterized by partial loss of this octahedral coordination and the disorder-induced formation of under-and over-coordinated Ti ions. This leads to the absence of the characteristic crystal-field splitting of unoccupied Ti 3d states into e g and t 2g like subbands. The optical characteristics of the amorphous phase are interpreted as a superposition of optical transitions that reflect the various local symmetries of the manifold of synthesizable crystalline TiO 2 phases. The linear optical properties, calculated within the independent-particle approximation, are found to be in good agreement with the available experimental data.

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Electronic excitations: Ab initio calculations of electronic spectra and application to zirconia ZrO2, titania TiO2 and cuprous oxide Cu2O

Cited by 21 publications

References 44 publications

Strong anisotropic influence of local-field effects on the dielectric response ofα-MoO3

Strong anisotropic influence of local-field effects on the dielectric response ofα-MoO3

Density functional theory study explaining the underperformance of copper oxides as photovoltaic absorbers

Fingerprints of order and disorder in the electronic and optical properties of crystalline and amorphous TiO2

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