  There has been considerable interest in properties of condensed matter at
finite temperature, including non-equilibrium behavior and extreme conditions
up to the warm dense matter regime. Such behavior is encountered, e.g., in
experimental time resolved x-ray absorption spectroscopy (XAS) in the presence
of intense laser fields. In an effort to simulate such behavior, we present an
approach for calculations of finite-temperature x-ray absorption spectra in
arbitrary materials, using a generalization of the real-space Green's function
formalism. The method is incorporated as an option in the core-level x-ray
spectroscopy code FEFF10. To illustrate the approach, we present calculations
for several materials together with comparisons to experiment and with other
methods.
