First-principles method for x-ray Thomson scattering including both elastic and inelastic features in warm dense matter

We show that the entire x-ray Thomson scattering (XRTS) spectrum, including both elastic and inelastic features, can be calculated from first principles in the framework of quantum perturbation theories. Our derivation shows that the elastic scattering feature in a warm dense regime is different from that of condensed matter at low temperature. In addition to the contribution from spatial fluctuations of electronic density, which dominates elastic scattering at low temperature, there is an extra contribution from partially occupied inner-shell states, which is important in the warm dense regime. Calculated XRTS of isochorically heated beryllium agrees well with previous experimental measurements, which may give this method a further edge on interpreting XRTS spectra compared to empirical modeling methods.