  The optical properties of particulate-matter aerosols, within the context of
exoplanet and brown dwarf atmospheres, are compared using three different
models: Mie theory, Modified Mean Field (MMF) Theory, and Discrete Dipole
Approximation (DDA). Previous results have demonstrated that fractal haze
particles (MMF and DDA) absorb much less long-wavelength radiation than their
spherical counterparts (Mie), however it is shown here that the opposite can
also be true if a more varying refractive index profile is used. Additionally,
it is demonstrated that absorption and scattering cross-sections, as well as
the asymmetry parameter, are underestimated if Mie theory is used. Although DDA
can be used to obtain more accurate results, it is known to be much more
computationally intensive; to avoid this, the use of low-resolution aerosol
models is explored, which could dramatically speed up the process of obtaining
accurate computations of optical cross-sections within a certain parameter
space. The validity of DDA is probed for wavelengths of interest for
observations of aerosols within exoplanet and brown dwarf atmospheres (0.2 to
15 micrometres). Finally, novel code is presented to compare the results of
Mie, MMF and DDA theories (CORAL: Comparison Of Radiative AnaLyses), as well as
to increase and decrease the resolution of DDA shape files accordingly
(SPHERIFY). Both codes can be applied to a range of other interesting
astrophysical environments in addition to exoplanet atmospheres, for example
dust grains within protoplanetary disks.
