  When matter is exposed to a high-intensity x-ray free-electron-laser pulse,
the x rays excite inner-shell electrons leading to the ionization of the
electrons through various atomic processes and creating high-energy-density
plasma, i.e., warm or hot dense matter. The resulting system consists of atoms
in various electronic configurations, thermalizing on sub-picosecond to
picosecond timescales after photoexcitation. We present a simulation study of
x-ray-heated solid-density matter. For this we use XMDYN, a Monte-Carlo
molecular-dynamics-based code with periodic boundary conditions, which allows
one to investigate non-equilibrium dynamics. XMDYN is capable of treating
systems containing light and heavy atomic species with full electronic
configuration space and 3D spatial inhomogeneity. For the validation of our
approach we compare for a model system the electron temperatures and the ion
charge-state distribution from XMDYN to results for the thermalized system
based on the average-atom model implemented in XATOM, an ab-initio x-ray atomic
physics toolkit extended to include a plasma environment. Further, we also
compare the average charge evolution of diamond with the predictions of a
Boltzmann continuum approach. We demonstrate that XMDYN results are in good
quantitative agreement with the above mentioned approaches, suggesting that the
current implementation of XMDYN is a viable approach to simulate the dynamics
of x-ray-driven non-equilibrium dynamics in solids. In order to illustrate the
potential of XMDYN for treating complex systems we present calculations on the
triiodo benzene derivative 5-amino-2,4,6-triiodoisophthalic acid (I3C), a
compound of relevance of biomolecular imaging, consisting of heavy and light
atomic species.
