Abstract: The band gap is a fundamental property of an insulator. There has been enormous interest to modify the band gap in semiconductors so as to manipulate the electronic properties. It is generally assumed that the energy gap of an insulator will decrease with increasing pressure and eventually leads to metallization. This is the primarily reason behind the tremendous efforts in the realization of metallic hydrogen. In contrast, a recent analysis of the refractive index of ice VII using the well-known Wemple model for semiconductors shows the band gap increases with high pressure. This is the motivation behind our study. To investigate this usual observation, density functional perturbation theory was used to compute the optical spectra (dielectric functions) of ice VII from which the refractive index can be obtained. We further apply the method to study the band gap closure of solid hydrogen, including the recently proposed phase -IV and the core level x-ray absorption of CO2 under high pressure. Recent results will be presented and discussed.   

 

Date&Time: September 23, 2013 (Monday), 9:30 - 10:30 a.m.
Location: 606 Conference Room