EQUATION OF STATE AND METALLIZATION OF ICE UNDER VERY HIGH-PRESSURE

The equation of state and the electronic bandstructure of ice have been calculated in the recently proposed high-pressure phase XI (anti-fluorite structure) by using the local-density approximation with the augmented-plane-wave method. The calculated pressure of metallization 1.76 TPa is in agreement with the value of 1.0-1.5 TPa conjectured by Besson (1986), but it is 2.5 times higher than that estimated by the classical Herzfeld theory (1927) and Thomas-Fermi-Dirac model. It has been also shown that the ionic model proposed for the ice XI phase is not adequate even for ultra-high pressure from the viewpoint of the bandstructure calculation.