The forbidden gap and insulator-metal transition under pressure

The behavior of the energy bands and the band gap width of a compressed insulator crystal is studied. The conduction band energy at the center of a face of the Brillouin zone first increases and then abruptly decreases upon an increase in compression, resulting in a collapse of the forbidden gap and in an insulator-metal (IM) transition. A model proposed for the mechanism of this transition interprets it to be a phase transition of order two and a half. The compression ratio and pressure at which an IM transition occurs in neon under pressure are predicted on the basis of nonempirical calculations of the valence and conduction bands. A simplified model suitable for calculating the metallization effect in more complex crystals is proposed.