Electronic, vibrational and related properties of group IV metal oxides by ab initio calculations (original) (raw)
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Journal of Alloys and Compounds, 2008
X-ray emission spectroscopy (XES) and X-ray photoelectron spectroscopy (XPS) methods were employed in the present paper to investigate the electronic structure of face-centred cubic (fcc) molybdenum dioxide, fcc-MoO 2 . For the mentioned compound, the XES O K␣ and Mo L 2,15 bands reflecting the valence O p-and Mo s,d-like states, respectively, were derived and compared on a common energy scale with the XPS valence-band spectrum. For comparison, the similar experimental studies of the electronic structure were made for a usual orthorhombic form of molybdenum trioxide, MoO 3 . Band-structure calculations of fcc-MoO 2 were made using the full potential linearized augmented plane wave (FP-LAPW) method. A rather good agreement of the experimental XES and XPS results and the theoretical FP-LAPW data for the electronic properties of fcc-MoO 2 has been achieved in the present paper. A new near-Fermi sub-band was detected on both the XES Mo L 2,15 band and the XPS valence-band spectrum when going from orthorhombic MoO 3 to fcc-MoO 2 . The FP-LAPW calculation reveals that the main contributors into the aforementioned sub-band of fcc-MoO 2 are the Mo 4d(e g ) states. Further, the FP-LAPW data indicate that the O 2p and Mo 4d(t 2g ) states contribute into both the central part and the bottom of the valence band of fcc-MoO 2 , while the Mo 4d(e g ) states contribute almost exclusively into the bottom of the valence band of the oxide. A significant portion of density of states (mainly Mo 4d(e g ) states) detected by the FP-LAPW calculation at the Fermi energy of fcc-MoO 2 indicates that the oxide is rather unstable.
Density functional theory study of MnO2, TiO2 and VO2
Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie, 2022
We investigate the structural stability of metal oxides β-MnO2, TiO2 and VO2 (MO2) which are used as catalyst in metal air batteries, using the density functional theory (DFT) within the generalized gradient approximation (GGA). Their mechanical property was determined to show the stability trend of the metal oxides catalyst. Cell parameters of the bulk structures of the MO2 are in reasonable agreement with the experimental values (deviations of approximately 0.8% and -3.1% for a and c, respectively, and of 1.6 % in the cell volume). Phonon dispersion curves show that rutile (R) TiO2 is the most stable structure since it does not have vibrations in the negative frequencies.
FIRST-PRINCIPLES LCAO CALCULATIONS ON 5D TRANSITION METAL OXIDES: ELECTRONIC AND PHONON PROPERTIES
Integrated Ferroelectrics, 2009
First-principles quantum chemistry calculations within the periodic linear combination of atomic orbitals (LCAO) formalism have been used to probe electronic and phonon properties of crystalline 5d transition metal oxides ReO 3 , ZnWO 4 and CaWO 4 . The obtained equilibrium crystal structure is in good agreement with known crystallographic data. Rhenium trioxide is correctly predicted to be a metal, whereas both tungstates-a wide gap insulating compounds. The phonon frequencies, calculated by the frozen phonon method, agree rather well with those obtained by infrared and Raman spectroscopies.
Equation of motion method for the electronic structure of disordered transition metal oxides
Computer Physics Communications, 1992
The equation of motion method is very well suited for studying the electronic density of states of disordered systems, especially those described by a tight binding Hamiltonian. The Hamiltonian problem is solved in direct space, hence the method can be applied to the systems with high substitutional disorder (oxygen vacancies, dopants), surfaces and interfaces and to study the local electronic environment in the presence of disorder. The presented version of the program was used to obtain the local, total and surface electronic density of states of rutile TiO 2_,~with up to x = 0.2 oxygen vacancies concentration.
High-throughput density-functional perturbation theory phonons for inorganic materials
Scientific data, 2018
The knowledge of the vibrational properties of a material is of key importance to understand physical phenomena such as thermal conductivity, superconductivity, and ferroelectricity among others. However, detailed experimental phonon spectra are available only for a limited number of materials, which hinders the large-scale analysis of vibrational properties and their derived quantities. In this work, we perform ab initio calculations of the full phonon dispersion and vibrational density of states for 1521 semiconductor compounds in the harmonic approximation based on density functional perturbation theory. The data is collected along with derived dielectric and thermodynamic properties. We present the procedure used to obtain the results, the details of the provided database and a validation based on the comparison with experimental data.
Journal of Solid State Chemistry, 2003
The development in theoretical condensed-matter science based on density-functional theory (DFT) has reached a level where it is possible, from ''parameter-free'' quantum mechanical calculations to obtain total energies, forces, vibrational frequencies, magnetic moments, mechanical and optical properties and so forth. The calculation of such properties are important in the analyses of experimental data and they can be predicted with a precision that is sufficient for comparison with experiments. It is almost impossible to do justice to all developments achieved by DFT because of its rapid growth. Hence, it has here been focused on a few advances, primarily from our laboratory. Unusual bonding behaviors in complex materials are conveniently explored using the combination of charge density, charge transfer, and electron-localization function along with crystal-orbital Hamilton-population analyses. It is indicated that the elastic properties of materials can reliably be predicted from DFT calculations if one takes into account the structural relaxations along with gradient corrections in the calculations. Experimental techniques have their limitations in studies of the structural stability and pressure-induced structural transitions in hydride materials whereas the present theoretical approach can be applied to reliably predict properties under extreme pressures. From the spin-polarized, relativistic full-potential calculations one can study novel materials such as ruthenates, quasi-one-dimensional oxides, and spin-, charge-, and orbitalordering in magnetic perovskite-like oxides. The importance of orbital-polarization correction to the DFT to predict the magnetic anisotropy in transition-metal compounds and magnetic moments in lanthanides and actinides are emphasized. Apart from the fullpotential treatment, proper magnetic ordering as well as structural distortions have to be taken into account to predict correctly the insulating behavior of transition-metal oxides. The computational variants LDA and GGA fail to predict insulating behavior of Mott insulators whereas electronic structures can be described correctly when correlation effects are taken into account through LDA þ U or similar approaches to explain their electronic structures correctly. Excited-state properties such as linear optical properties, magneto-optical properties, XANES, XPS, UPS, BIS, and Raman spectra can be obtained from accurate DFT calculations.
D-D Spectra of Transition Metal Oxides by Effective Crystal Field Method
Journal of Molecular Catalysis A-chemical, 1997
The effective crystal field (ECF) method is applied to d-d excitations in metal oxides of the first transition series as measured by optical and EELS techniques. The computations are performed in the framework of the cluster approximation. The octahedral clusters are employed to simulate the transition metal ions in the bulk, the square pyramidal ones for simulation of the ions on the (100) crystal surfaces. A fair agreement between the calculation performed without additional parameter adjustment and experiment is reached when the effect of the Madelung potential on the electronic structure of the oxygens surrounding the transition metal ion and by this on the effective crystal field induced by them is carefully taken into account.
2013
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. I. INTRODUCTION α-MoO 3 is the thermodynamically stable phase of the molybdenum trioxide in ambient conditions and is described in an orthorhombic unit cell (space group Pbnm) with the cell parameters a = 3.9624(1), b = 13.860(2), c = 3.6971(4) Å. 1 The structure consists in 2 / ∞ [MoO 3 ] sheets that are orientated perpendicular to the [010] y axis, and are held together by van der Waals interactions (Fig.
Systematic Analysis of ARPES Spectra of Transition-Metal Oxides: Nature of Effective d Band
Journal of the Physical Society of Japan, 2009
We have performed systematic tight-binding (TB) analyses of the angle-resolved photoemission spectroscopy (ARPES) spectra of transition-metal (TM) oxides AM O3 (M = Ti, V, Mn, and Fe) with the perovskite-type structure and compared the obtained parameters with those obtained from configuration-interaction (CI) cluster-model analyses of photoemission spectra. The values of ǫ d −ǫp from ARPES are found to be similar to the charge-transfer energy ∆ from O 2p orbitals to empty TM 3d orbitals and much larger than ∆ − U/2 (U : on-site Coulomb energy) expected for Mott-Hubbardtype compounds including SrVO3. ǫ d − ǫp values from ab initio band-structure calculations show similar behaviors to those from ARPES. The values of the p − d transfer integrals to describe the global electronic structure are found to be similar in all the estimates, whereas additional narrowing beyond the TB description occurs in the ARPES spectra of the d band.