Theoretical Study On Electronic Structures And Properties Of Solide Carbon Dioxide

In this dissertation, details of the electron structures and properties of the nine kinds of solid CO2 were studied using CASTEP code by means of first-principle calculations based on the plane-wave pseudo-potential. The eight of nine kinds of CO2 are analog to SiO2:α-quartz,β-quartz,α-cristobalite,β-cristobalite, C9, hexagonal, stishovite, P212121(this structure does not exist in SiO2). The other one is cubic-pyrite structure.We systematically investigated the equilibrium energies, density of states, and elastic properties of the solid CO2 by means of plane wave pseudo-potential method with generalized gradient approximation and local density approximation based on density function theory. The calculated lattice parameters ofα-quartz was consistent with Serra et al.'s calculation values. The equilibrium energies calculation indicates thatβ-cristobalite structure is more energetically stable under the ambient condition, which was consistent with the reffrences.The computational elastic constants results showed they were mechanically stable exception of stishovite and cubic-pyrite. The hardness for these structures has been evaluated according to the intrinsic hardness calculation theory of covalent crystal based on the Mulliken overlap population. The results indicated that these phases are none of superhard materials. Furthermore, we clarified the stereochemical effect of the lone-pair electrons on the hardness of the solid CO2.