A Nebula in Your Computer: Simulating the Physics and Chemistry of an H <Emphasis Type="SmallCaps">ii</Emphasis> Region

In this contribution we discuss about numerical modeling of nebulae. In particular we emphasize on the dynamical evolution of an H II region and on the chemical structure of a Photodissociation region. We do this by using the Smoothed Particles Hydrodynamics code SEREN and the recently developed astrochemistry code 3D-PDR. We show an example application by simulating a cometary globule using these two codes.