Pressure dependent electronic properties of MgO polymorphs: A first-principles study of Compton profiles and autocorrelation functions

The first-principles periodic linear combination of atomic orbitals method within the framework of density functional theory implemented in the CRYSTAL06 code has been applied to explore effect of pressure on the Compton profiles and autocorrelation functions of MgO. Calculations are performed for the B1, B2, B3, B4, B8_1 and h-MgO polymorphs of MgO to compute lattice constants and bulk moduli. The isothermal enthalpy calculations predict that B4 to B8_1, h-MgO to B8_1, B3 to B2, B4 to B2 and h-MgO to B2 transitions take place at 2, 9, 37, 42 and 64 GPa respectively. The high pressure transitions B8_1 to B2 and B1 to B2 are found to occur at 340 and 410 GPa respectively. The pressure dependent changes are observed largely in the valence electrons Compton profiles whereas core profiles are almost independent of the pressure in all MgO polymorphs. Increase in pressure results in broadening of the valence Compton profiles. The principal maxima in the second derivative of Compton profiles shifts towards high momentum side in all structures. Reorganization of momentum density in the B1 to B2 structural phase transition is seen in the first and second derivatives before and after the transition pressure. Features of the autocorrelation functions shift towards lower r side with increment in pressure.Comment: 19 pages, 8 figures, accepted for publication in Journal of Materials Scienc

Towards a refinement of bonding features in MgO from directional Compton profiles

International audienceAdhesive properties of metals on oxide substrates, such as MgO, critically depend on the effective covalent character of metal-oxygen. In ionic solids the anisotropy among directional Compton profiles was shown to be strongly dependent upon the iono-covalent character of cohesive interactions. A systematic study of momentum density was thus undertaken for MgO, both experimental and theoretical. Reliable DCPs were obtained at ESRF, anisotropies being in fair agreement with Hartree-Fock calculations. In order to refine coupling parameters among valence orbitals, a three-dimensional (3D) reconstruction of momentum density is necessary. Various approaches are considered besides spherical harmonics reconstruction, we propose a simple and efficient Gaussian fit of DCPs, followed by an extrapolation to the 3D momentum density. Preliminary results are discussed

Analytical reconstruction of momentum density from directional compton profiles

International audienceAn alternative method for reconstruction of three-dimensional momentum density from directional Compton profiles is proposed and successfully applied to theoretical data on magnesium oxide (with a random noise added). The method consists of obtaining a compact analytical model for the reconstructed (Formula presented) from the least-squares fit directly on the directional profiles. The result is compared, together with a standard numerical-based reconstruction, to the theoretical momentum density from which the profiles were calculated. © 1999 The American Physical Society