Comment on ''Strong-coupling theory of hydrogen plasmas''

The integral equations applied to a hydrogen plasma by Yan, Tsai, and Ichimaru [Phys. Rev. A 43, 3057 (1991)] are shown to become inappropriate when the plasma begins to have a bound state which brings about a low degree of ionization: the bound-state contribution to forming an ion should be taken in the form needed to induce changes in the bare ion-ion and electron-ion interactions. Moreover, their definition of a degree of ionization shows an abrupt change when a bound state disappears, and this discontinuity is associated with a phase transition. However, this discontinuity in the ionization may not be a real one, since it is possible to define a degree of ionization, which remains continuous in the change from a bound to a continuum state