Fractal Particle Opacity Toolkit

Python utilities to compute and store dust opacities and scattering properties for porous fractal particles using Optool and scattnlay.

This project wraps two main backends:

• Optool for Mie and MMF opacities and optionally the full scattering matrix
• scattnlay for layered sphere scattering and optionally the full scattering matrix

It provides a Particle class that:

• derives bulk and fractal properties from a small parameter set
• runs opacity calculations via Optool and scattnlay
• saves results in a robust folder format and can load them back later

Features

• Fractal particle model based on fractal dimension D, prefactor kf, monomer radius a0, and characteristic radius Rc
• Derived quantities: mass, mean density, filling factor, porosity, radius of gyration
• Optional subdivision into N radial shells with wavelength dependent effective refractive indices
• Compute opacities:
  • Optool Mie: RunMie()
  • Optool MMF: RunMMF()
  • scattnlay layered scattering: RunScatt()
• Optional scattering matrix output for Optool and scattnlay
• Save and load results safely even if some outputs are missing

Requirements

Python packages used in the code: subprocess shlex numpy pandas matplotlib.pyplot scattnlay re pathlib json

External dependency:

• Optool executable available on your system PATH as optool

Notes:

• The code calls optool via subprocess. Make sure the optool command is available in your environment.

Configuration

Global Optool settings are controlled via:

OPTOOL_SETTINGS = {
    "lmin": 0.1,     # micron
    "lmax": 1000,    # micron
    "nl": 100,
    "method": "mie",
    "NANG": 180
}