but little data exists shortward of $\sim 0.1 \mu$m. Theoretical relationships between the bulk grain properties and the photoionization cross sections of the constituent atoms can be used to create complete refractive index data for grain materials when combined with the Kramers-Kronig relations. Refractive index data for astronomical silicate, amorphous carbon, and graphite, based on @Martin1991, @Rouleau1991, and @Laor1993 are included in the  download. Opacity data for PAHs from Volk (private communication, based on data from [@Bregman1989], [@Desert1990], and [@Schutte1993]), @Li2001, and @Draine2007 are built into the code.

The Mie code includes the possibility to mimic mixtures of materials in grains using effective medium theory (EMT). The following EMT recipes are supported by : @Bruggeman1935, @Stognienko1995, and @Voshchinnikov1999 (based on the theory in [@Farafonov2000]). The first two are appropriate for randomly mixed grain materials, while the latter is intended for layered grains.  includes a refractive index file for vacuum which enables modeling fluffy grains when combined with other materials using an EMT.

@Abel2008 discusses how our treatment, which is based on elementary processes as as possible, affects results for PDR simulations. Conventional PDR codes use precomputed integrals of photoionization or photodissociation cross sections over an SED representative of the Galactic 