140 GPaحتما لضغطPREMعندضغوط النموذج(CaO)و الكالسيوم (MgO)المساهمة في دراسة الخصائص البنيوية، المرونية والتيرموديناميكية لأكسيدي المنغنيزيوم

Abstract

In our work, we studied some parameters of the structural, elastic and tyodynamic properties of magnesium oxide (MgO) and calcium (CaO) at pressures of the PREM model. By calculation using density functional theory (DFT) with the generalized gradient approximation (GGA), as we chose from among several functions the modern function PBEsol .Starting with geometric optimization, we confirmed that the phase transformation of calcium oxide from phase B1 to B2 occurs at 59.2 GPa, while manganese oxide remains stable in its first phase, B1. Despite the slight difference in our results from the previous study, whether experimental or computational, especially at zero pressure, the agreement confirms the validity of these results. Also, after we chose the degree of the polynomials most appropriate to the change of these parameters with changes in pressure, we were able to accurately compare the parameters of these two oxides and between them and what is provided by the PREM model, in addition to determining the values of these parameters at the basic discontinuities in the subsurface to contribute to the global data base.The agreement is also clear for the Debye temperature of both oxides, and the values of both the heat capacity with constant volume and the entropy at 300 K for magnesium oxide. While we were not able to compare the results of our calculation for both internal and free energy of oxides and the tow thermodynamic parameters for calcium oxide with the results of previous studies because they are not available.