Calculation of near K edge x-ray absorption spectra and hydrogen bond network in ice XIII under compression

Abstract

The hydrogen bond network, oxygen K edge x-ray absorption spectra (XAS), and electronic structure of ice XIII under compression have been extensively studied by density functional theory (DFT). We showed that DFT methods yield a ground state consistent with previous neutron scattering experiment and a few low-enthalpy metastable states are likely to coexist from the total enthalpy calculations. Oxygen K edge XAS of four low-enthalpy configurations was studied with the aim to shed light on the local structure in these configurations. We demonstrated that pre-edge of oxygen K edge XAS is a common feature appearing in all these four structures while major spectral differences exist in the main peak area. Therefore, we arrived at the conclusion that the main peak is more sensitive to the local hydrogen bond environment and could be used as an effective tool to distinguish these four configurations. We also found that the pre-edge has main contribution from O 1s-4a1 transitions and its intensity was suppressed by pressure while the main peak is mostly coming from O 1s-2b2 transitions.