  We have developed a general model for determining density-dependent effective
dielectronic recombination (DR) rate coefficients in order to explore
finite-density effects on the ionization balance of plasmas. Our model consists
of multiplying by a suppression factor those highly-accurate total zero-density
DR rate coefficients which have been produced from state-of-the-art theoretical
calculations and which have been benchmarked by experiment. The suppression
factor is based-upon earlier detailed collision-radiative calculations which
were made for a wide range of ions at various densities and temperatures, but
used a simplified treatment of DR. A general suppression formula is then
developed as a function of isoelectronic sequence, charge, density, and
temperature. These density-dependent effective DR rate coefficients are then
used in the plasma simulation code Cloudy to compute ionization balance curves
for both collisionally ionized and photoionized plasmas at very low (ne = 1
cm^-3) and finite (ne=10^10 cm^-3) densities. We find that the denser case is
significantly more ionized due to suppression of DR, warranting further studies
of density effects on DR by detailed collisional-radiative calculations which
utilize state-of-the-art partial DR rate coefficients. This is expected to
impact the predictions of the ionization balance in denser cosmic gases such as
those found in nova and supernova shells, accretion disks, and the broad
emission line regions in active galactic nuclei.
