Local characteristics of the electronic structure of MgO: LCAO and plane-wave calculations (original) (raw)
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X-ray and Electron Diffraction Study of MgO
Acta Crystallographica Section B Structural Science, 1998
Precise X-ray and high-energy transmission electron diffraction methods were used for the study of electron density and electrostatic potential in MgO crystals. The structure amplitudes were determined and their accuracy estimated using ab initio Hartree-Fock structure amplitudes as criteria. The electrostatic potential distributions, reconstructed using Fourier series from both X-ray and electron diffraction data, are in satisfactory mutual agreement and are similar to the theory. They, however, suffer from restricted experimental resolution and, therefore, the reconstruction of the electrostatic potential via an analytical structural model is preferable. The x model of electron density was adjusted to X-ray experimental structure amplitudes and those calculated by the Hartree-Fock method. The electrostatic potential, deformation electron density and the Laplacian of the electron density were calculated with this model. The critical points in both experimental and theoretical model electron densities were found and compared with those for procrystals from spherical atoms and ions. A disagreement 11 concerning the type of critical point at (Z,Z,0) in the area of low, near-uniform electron density is observed. It is noted that topological analysis of the electron density in crystals can be related with a close-packing concept.
2018
In this work we calculated MgO ab initio X-ray Absorption and Emission spectra using the Full Potential Linearized Augmented Plane Wave method within the Density Functional Theory formalism. The X-ray Absorption and Emission spectra for the K and L2;3 edges of Mg and O atoms were calculated including a core hole in order to study the electronic structure of valence and conduction bands of the system. Both kinds of spectra were compared with experimental data obtaining a very good agreement and the improvement in the spectra due to the use of Tran Blaha modified Becke-Johnson (TB-mBJ)potential is manifested. This potential describes better the insulator properties, produces a band gap that is in good agreement with the experimental value and improves the intensities and the structure of the spectra. Was interesting to find the presenceof Mg d states below the Fermi energy in the equilibrium volume of MgO. The XANES experiments were better reproduced by introducing the full core hole ...
Electronic structure of the [MgO3]+ cation
The Journal of Chemical Physics, 2012
Accurate ab initio calculations are performed to investigate the stable isomers of [MgO 3 ] + and its lowest electronic states at both molecular and asymptotic regions. The calculations are done using large basis sets and configuration interaction methods including the complete active space self-consistent field, the internally contracted multi-reference configuration interaction, the standard coupled cluster (RCCSD(T)) approaches and the newly implemented explicitly correlated coupled cluster method (RCCSD(T)-F12). The presence of three stable forms is predicted: a cyclic global minimum c-MgO 3 + , which is followed by a quasi-linear isomer, l2-MgO 3 +. A third isomer of C s symmetry (l1-MgO 3 +) is also found. Moreover, we computed the one-dimensional cuts of the sixdimensional potential energy surfaces of the lowest doublet and quartet electronic states of [MgO 3 ] + along the R MgO and R OO stretching coordinates covering both the molecular and the asymptotic regions. These curves are used later for discussing the metastability of this cation and to propose plausible mechanisms for the Mg + + O 3 atmospherically important ion-molecule reaction and related reactive channels.
The Quantum-Topological Analysis of Electron Density in Mgo Crystal
Nihon Kessho Gakkaishi, 1995
Precise X-ray and high-energy transmission electron diffraction methods were used for the study of electron density and electrostatic potential in MgO crystals. The structure amplitudes were determined and their accuracy estimated using ab initio Hartree-Fock structure amplitudes as criteria. The electrostatic potential distributions, reconstructed using Fourier series from both X-ray and electron diffraction data, are in satisfactory mutual agreement and are similar to the theory. They, however, suffer from restricted experimental resolution and, therefore, the reconstruction of the electrostatic potential via an analytical structural model is preferable. The x model of electron density was adjusted to X-ray experimental structure amplitudes and those calculated by the Hartree-Fock method. The electrostatic potential, deformation electron density and the Laplacian of the electron density were calculated with this model. The critical points in both experimental and theoretical model electron densities were found and compared with those for procrystals from spherical atoms and ions. A disagreement 11 concerning the type of critical point at (Z,Z,0) in the area of low, near-uniform electron density is observed. It is noted that topological analysis of the electron density in crystals can be related with a close-packing concept.
Analysis of the MgO structure factors
Physical Review B, 1999
The results of recent measurements ͓Zuo et al., Phys. Rev. Lett. 78, 4777 ͑1997͔͒ of some low-order structure factors of MgO have been reinterpreted by means of an ab initio calculation and of two models of charge density. The discrepancies between the calculated and the experimental structure factors are 3% for the 111 reflection and smaller than 1% in the other cases. The charge transfer, which is well defined in the framework of the ab initio method that we have used, is found to be equal to 2. On the other hand, refinements of the model parameters yield values of the charge transfer ranging from 1.81 to 1.92, with little change on the R factor. The electron density of the oxygen ion in the crystal has also been deduced from the model analysis of the experimental data. The resulting distribution is in excellent agreement with that obtained by the ab initio calculation. These conclusions differ from those of the preceding analysis of the same experimental data performed by Zuo et al. ͓S0163-1829͑99͒02436-4͔
The bonding in the low-lying states of MgO+2
Chemical Physics Letters, 1993
The 'A, ground state of MgO,+ is of Mg'+O; character with an Mg+-0, binding energy of 23.3 kcal/mol. The linear 'Z-state, which is bound by a charge-quadrupole interaction, has a significantly smaller binding energy (5.9 kcal/mol). Unlike many Mg+-ligand systems, there are no observable bound-bound transitions for Mg02+ below 35000 cm-'.
Study of the surface electronic structure of MgO bulk crystals and thin films
Surface Science, 1996
The electronic structures of the surfaces of MgO single crystals, oxidized Mg polycrystals and oxidized Mg films grown by molecular beam epitaxy on Si(100) surfaces were studied using several techniques. These include metastable impact electron spectroscopy (MIES), ultraviolet photoelectron spectroscopy (UPS (He I)), and X-ray photoelectron spectroscopy (XPS). Spectra of oxidized Mg layers on Si(100) show additional features to those obtained for cleaved MgO crystals. These spectral features are attributed to dissociative adsorption of oxygen at bulk oxygen sites. Weak heating of the oxidized Mg layers removes these features and the electronic spectra for all three studied systems become similar. However, the experimental MIES and UPS spectra, both arising mainly from the ionization of the O 2p orbitals, have different structures. They are interpreted on the basis of ab initio Hartree-Fock and density functional calculations of the electronic structures of the ideal MgO(100) surface. It is shown, that the differences in the spectra can be understood by taking into account that UPS spectra reflect the density of electronic states within several surface layers, whereas MIES probes the surface states which are the most extended into the vacuum.
Applied Nanoscience, 2018
From experimental investigations of the bandgaps of magnesium oxide (MgO) nanostructures, the results show that band-gap narrowing occurred as the physical dimension of the MgO crystallites decrease. This is in contrast to other metal oxides such as ZnO. To obtain insights on this observed phenomenon, the first-principle studies using density functional theory were carried out. The strategy used here is different from the normal theoretical studies, such that information of the structural characterization obtained from experimental X-ray diffraction (XRD) data via the Rietveld method was used in the calculations. This is important, because nanostructures do not possess the same crystal parameters as the bulk and accurate real structural parameters should be used in the calculations. Based on these values, the crystal structures were simulated and the electronic band structures were calculated within the density functional theory (DFT). Results from the density of state (DOS) studies shows that the band-gap narrowing is due to the shifting of the valence and conduction bands. From our theoretical results, we can conclude that the narrowing of the bandgaps of MgO nanostructures is a consequence of the increase of their lattice parameters. The calculated results exhibit this trend and are in good agreement with the experimental results.