Band structure and transport properties of CrO2

The local-spin-density approximation is used to calculate the energy bands of both the ferromagnetic and paramagnetic phases of metallic CrO2. The Fermi level lies in a peak in the paramagnetic density of states, and the ferromagnetic phase is more stable. As predicted by Schwarz, the Fermi level lies in an insulating gap in the minority-spin bands between oxygen p and chromium d states (''half-metallic'' behavior). The resulting magnetic moment is 2 mu(B) per Cr atom, in agreement with experiment. The A(1g) Raman frequency is predicted to be 587 cm(-1). Drude plasma frequencies are of order 2 eV, as seen experimentally by Chase. The measured resistivity is used to find the electron mean free path l, which is only a few angstroms at 600 K, but, nevertheless, resistivity continues to rise as temperature increases. This puts CrO2 into the category of ''bad metals'' in common with the high-T-c superconductors, the high-T metallic phase of VO2, and the ferromagnet SrRuO3. In common with both SrRuO3 and Sr2RuO4, the measured specific-heat parameter gamma is higher than band theory predicts by a renormalization factor close to 4.