Utility of High Performance Computing Facilities for the Calculation of the Theoretical X-ray Absorption Spectra of Solids

Two cases demonstrating the utility of high performance computing to calculate X-ray absorption spectra (XAS) of solids are discussed. The X-ray absorption spectra of high pressure ices II, VIII, and IX have been computed with the Car Parrinello plane wave pseudopotential method. XAS for the intermediate structures obtained from uniaxial compression of hexagonal graphite along the c-axis are also studied. Whenever possible, comparisons to available experimental results are made. The reliability of the computational methods for the calculations of the XAS for these structures is discussed.