A nebula in your computer: simulating the physics and chemistry of an
  HII region
  In this contribution we discuss about numerical modeling of nebulae. In
particular we emphasize on the dynamical evolution of an HII region and the
chemical structure of a Photodissociation region. We do this using the Smoothed
Particles Hydrodynamics code SEREN and the recently developed astrochemistry
code 3D-PDR, respectively. We show an example application by simulating a
cometary globule using these two codes.
