Radiative feedback and cosmic molecular gas: numerical method
  We present results from self-consistent 3D numerical simulations of cosmic
structure formation with a multi-frequency radiative transfer scheme and
non-equilibrium molecular chemistry of 13 primordial species (e-, H, H+, H-,
He, He+, He++, H2, H2+, D, D+, HD, HeH+), performed by using the simulation
code GADGET. We describe our implementation and show tests for ionized sphere
expansion in a static and dynamic density field around a central radiative
source, and for cosmological abundance evolution coupled with the cosmic
microwave background radiation. As a demonstrative application of radiative
feedback on molecular gas, we run also cosmological simulations of early
structure formation in a ~1Mpc size box. Our tests agree well with analytical
and numerical expectations. Consistently with other works, we find that
ionization fronts from central sources can boost H2 fractions in
shock-compressed gas. The tight dependence on H2 lead to a corresponding boost
of HD fractions, as well. We see a strong lowering of the the typical molecular
abundances up to several orders of magnitudes which partially hinders further
gas collapse of pristine neutral gas, and clearly suggests the need of
re-ionized gas or metal cooling for the formation of the following generation
of structures.
