Theoretical calculations for solid oxygen under high pressure
Abstract
The crystal structure of solid oxygen at low temperatures and at pressures up to 7 GPa is studied by theoretical calculations. In the calculations, the adiabatic potential of the crystal is approximated by a superposition of pair-potentials between oxygen molecules calculated by an ab initio method. The monoclinic α structure is stable up to 6 GPa and calculated lattice parameters agree well with experiments. The origin of a distortion and that of an anisotropic lattice compressibility of the basal plane of α-O2 are clearly demonstrated. In the pressure range from 6 to 7 GPa, two kinds of structures are proposed by x-ray diffraction experiments: the α and orthorhombic δ structures. It is found that the energy difference between these structures becomes very small in this pressure range. The relation between this trend and the incompatible results of x-ray diffraction experiments is discussed.
- Publication:
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Journal of Physics Condensed Matter
- Pub Date:
- August 2008
- DOI:
- 10.1088/0953-8984/20/33/335219
- arXiv:
- arXiv:0807.3793
- Bibcode:
- 2008JPCM...20G5219N
- Keywords:
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- Condensed Matter - Materials Science
- E-Print:
- 12 pages, 6 figures