Influence of Electron Correlation Effects on Bulk MgO Energetic Properties (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.
International Journal of Trend in Scientific Research and Development, 2020
Expression for the Bulk modulus and its Pressure derivatives have been derived and reduced to the limit of infinite pressure. The Pressure dependence of thermal expensively and the Grüneisen Parameter both are determined using the formulations which satisfy the thermodynamic constraints at infinite pressure. Values of Bulk modulus and its Pressure derivative are also obtained for the entire range of Temperatures and Pressures considered in the present study. We have also investigated the Thermo elastic Properties of MgO at high Temperature and High Pressures using the results based on the EOS. The method based on the calculus in determinates for demonstrating that on the physically acceptable EOS Satisfy the identities for the pressure derivatives of bulk modulus Materials.
All-electron and pseudopotential study of MgO: Equation of state, anharmonicity, and stability
We have studied the high-pressure behavior of periclase ͑MgO͒ using density functional simulations within the generalized gradient approximation. The static and thermal ( P-V-T) equation of state, B1-B2 transition pressure, elastic constants, Grüneisen parameter, and the intrinsic anharmonic parameters were calculated from static and ab initio molecular dynamics simulations. The simulations were performed using the projector augmented-wave and pseudopotential methods with different descriptions of the Mg atom ͑''small core'' and ''large core''͒. The errors of large-core pseudopotentials increase with pressure and are mainly due to the overlap between the Mg semicore ͑2p͒ orbitals and the valence orbitals, both of the same Mg atom and of the neighboring O atoms, rather than core deformation or core-core overlap effects. In agreement with previous works, we find that MgO remains in the B1 ͑''NaCl''͒ structure at all pressures existing within the Earth, and transforms into the CsCl-type structure at 509 GPa. Direct ab initio calculations avoid the simplifying assumptions inherent to many empirical treatments of thermoelasticity and allowed us to assess some of the common assumptions. We present a detailed qualitative analysis of the effects of intrinsic anharmonicity and analyze the validity of the Mie-Grüneisen approximation at high temperatures.
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.
Lattice Dynamics of MgO at High Pressure: Theory and Experiment
Physical Review Letters, 2006
The longitudinal acoustic and optical phonon branches along the ÿ-X direction of MgO at 35 GPa have been determined by inelastic x-ray scattering using synchrotron radiation and a diamond-anvil cell. The experimentally observed phonon branches are in remarkable agreement with ab initio lattice dynamics results. The derived thermodynamic properties, such as the specific heat C V and the entropy S are in very good accord with values obtained from a thermodynamically assessed data set involving measured data on molar volume, heat capacity at constant pressure, bulk modulus and thermal expansion.
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
Charge Density of MgO: Implications of Precise New Measurements for Theory
Physical Review Letters, 1997
A tenfold improvement in the accuracy of measured low-order structure factors for MgO has been achieved using the convergent beam electron diffraction technique. These results allow a meaningful comparison to be made with the latest calculations. We find that the MgO charge density can be described by a superposition of spherical Mg 21 and O 22 ions, but that a small nonspherical distortion of Mg and O is observable in both experiment and theory. The experimental charge distribution of O 22 is more diffuse than the theory, which may be due to the breathing effect of O 22 in a vibrating lattice. [S0031-9007(97)
Pressure – Volume Behavior of Mgo At Elevated Temperatures And Pressure
The isothermal equations of state (EOS) of solids have played an important role in the field of high-pressure physics. An isothermal EOS is used to study the relationship between pressure P and volume compression at a given temperature. Equation of state is also used to study the isothermal bulk modulus BT and its pressure derivativesBò andBò`, respectively. These derivatives are used as input parameters in various phenomenological forms. The values ofBò`for various solids are much less accurate as compared to the values of B T andBò. In the present work we consider six different forms of EOS which contain B T andBò only. Using these forms we have studied the pressure-volume relationships for MgO at room temperature and also at elevated temperatures (500-1500 K). Periclase is the end member of the (Mg, Fe) O solid solution series. A precise description of the pressure, volume and temperature (P_V_T) relationship of MgO is therefore essential. Seema Rajput