  The effect of the absorption of hard X-ray photons on the solid-state
dynamics, at energies below the defect creation threshold, is considered.
First, it is shown that due to the sensitivity to parameter choices, the
present state of the theoretical description of photon-electron-lattice
coupling cannot decide on whether the local energy deposition due to the
absorption of single photons leads to an acceleration of atomic dynamics at
fluences before macroscopic effects due to sample heating set in. Second, a
direct study of the dynamics under different incident photon fluxes by
atomic-scale X-ray Photon Correlation Spectroscopy (aXPCS) is reported, which
provides an upper bound of 0.005 additional atomic jumps per absorbed photon of
8 keV. The relevance of such considerations for emergent experimental methods,
such as studying atomic dynamics using X-rays as probes, is pointed out.
