Metallization of solid iodine in phase I: X-ray diffraction measurements, electrical resistance measurements, and ab initio calculations

Metallization of solid iodine has carefully been investigated using X-ray diffraction (XRD) measurements, electrical resistance measurements, and ab initio calculations based on the density functional theory. The XRD and electrical resistance measurements have clarified that iodine takes the insulator-to-metal transition at 1416GPa in the diatomic molecular solid phase. The ab initio calculations have predicted that the electronic band gap decreases monotonically with increasing pressure, and it completely closes at around 1112GPa in the molecular phase, which is consistent with the experimental observations. At the metallization, we also experimentally and theoretically found the anomaly in the decrease of lattice constants along with pressurization.