  We have developed a new model for the astrochemical structure of a viscously
evolving protoplanetary disk that couples an analytic description of the disk's
temperature and density profile, chemical evolution, and an evolving dust
distribution. We compute evolving radial distributions for a range of dust
grain sizes, which depend on coagulation, fragmentation and radial drift
processes. In particular we find that the water ice line plays an important
role in shaping the radial distribution of the maximum grain size because ice
coated grains are significantly less susceptible to fragmentation than their
dry counterparts. This in turn has important effects on disk ionization and
therefore on the location of dead zones. In comparison to a simple constant
gas-to-dust ratio model for the dust as an example, we find that the new model
predicts an outer dead zone edge that moves in by a factor of about 3 at 1 Myr
(to 5 AU) and by a factor of about 14 by 3 Myr (to 0.5 AU). We show that the
changing position of the dead zone and heat transition traps have important
implications for the formation and trapping of planets in protoplanetary disks.
Finally, we consider our results in light of recent ALMA observations of HL Tau
and TW Hya.
