Ab initio calculations were performed on CrO _2 to study its behavior and possible similarity to silica under high pressures. At the rutile→CaCl _2-type phase transition, the lattice constants, cell volume and total energy change continuously, indicating the second-order nature of the phase transition, consistent with the experimental observations. The current calculations have demonstrated that the rutile→CaCl _2-type phase transition is driven by the softening of the Raman active B 1g mode, weakly coupling with the elastic shear modulus C s. Further phase transitions of CrO _2 to denser packed phases of α-PbO _2-type and pyrite have been well predicted by total energy calculations. Our electronic calculations revealed that CrO _2 is still a half-metallic ferromagnet up to pressure of 95 GPa. The present results confirm the analogy of the phase sequence between silica and CrO _2 at high pressures.
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