Equation of state and opacities for hydrogen atmospheres of strongly   magnetized cooling neutron stars
  We study partially ionized hydrogen plasma at temperatures T = 10^{5.5}-10^{6.5} K and magnetic fields B = 10^{12}-10^{13} G, typical of photospheres of isolated neutron stars. We construct an analytic model of the plasma free energy and derive a generalized Saha equation which is used to obtain the opacities. 
A. Y. Potekhin, Yu. A. Shibanov (Ioffe Phys.-Tech. Institute,   St.-Petersburg), J. Ventura (Univ. Crete, Heraklion)