Pure hydrogen weak D-type ionization front. Density a), temperature b), velocity c), and degree of ionization d) are depicted. A CLOUDY simulation (red dashed lines) is compared with a TPCI simulation (blue solid lines). Initial conditions are given by the gray dotted lines. In panel c) the speed of sound is shown by the black solid line. The TPCI simulation agrees well with the independent CLOUDY simulation. Small oscillations in the high-density region that can be seen in panel c) do not affect the solution significantly.