Theoretical study of structures of solid oxygen under high pressure

The structure of solid oxygen under high pressure is studied up to 6GPa with no empirical parameters. The potential of the crystal is described by superposition of O-2 pair potentials calculated by the ab initio method. Structural optimization is achieved with this potential energy surface. The monoclinic structure is stable up to 6GPa and a monoclinic-orthorhombic structural transition is not found. The pressure dependence of lattice constants agrees with the result of recent X-ray diffraction experiments.