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→B8 1 , h-MgO→B8 1 , B3→B2, B4→B2 and h-MgO→B2 transitions take place at 2, 9, 37, 42 and 64 GPa respectively. The high pressure transitions B8 1 →B2 and B1→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→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.
The electronic band structure and density of states (DOS) of B2-phase cadmium oxide (CdO) are computed following the firstprinciples linear combination of atomic orbitals method applying the CRYSTAL code. The PBE correlation functional coupled with Becke's ansatz for exchange is considered for calculations. The electronic band structure and DOS are examined considering HF, B3LYP and hybrid schemes. Hybrid functionals are used with 25, 15, 10 and 5% mixing of Fock exchange with PBE-GGA. Depending on the correlation functionals, and different mixings in the hybrid schemes, B2-phase CdO may have an indirect positive band gap, a negative band gap or a zero gap. The effect of pd repulsion originating from pd hybridisation is visible in the calculated band structures.
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