PAH size

TODO: merge PAH pages into one single page PAH_heating_and_chemistry, PAH_size, PAH_chemical_network

To change the default PAH size, in the Parameter.in file:

.true.           ! other_PAH
other_name       ! PAH_name : the name of your PAH
150              ! PAH_NC    : number of carbon atoms in the PAH
30               ! PAH_NH    : number of hydrogen atoms in the PAH

A list of PAHs are listed in this database: [http://www.astrochem.org/pahdb/]

For the abundance, it is set by:

0.01        ! fPAH        [-]     : PAH abundance with respect to ISM

The ISM abundance is 3e-7