  We simulate the formation of a large X-ray cluster using a fully 3D
hydrodynamical code coupled to a Particle-Mesh scheme which models the dark
matter component. We focus on a possible decoupling between electrons and ions
temperatures. We then solve the energy transfer equations between electrons,
ions and neutrals without assuming thermal equilibrium between the three gases
(T_e <> T_i <> T_n). We solve self-consistently the chemical equations for an
hydrogen/helium primordial plasma without assuming ionization-recombination
equilibrium. We find that the electron temperature differs from the true
dynamical temperature by 20% at the Virial radius of our simulated cluster.
This could lead marginally to an underestimate of the total mass in the outer
regions of large X-ray clusters.
