Reducing shape errors in the discrete dipole approximation using effective media

Area of Science:

• Computational physics
• Optical properties of materials
• Atmospheric science

Background:

• Discrete dipole approximation (DDA) is crucial for simulating particle optical properties.
• High accuracy DDA requires significant computational resources, especially for large or complex particles.
• Black-carbon (BC) aerosols present challenges due to their size and structure.

Purpose of the Study:

• To investigate the smoothing of DDA discretization using the effective medium approximation (EMA) for boundary dipoles.
• To enhance the accuracy and efficiency of DDA simulations for optical properties.
• To apply and validate the EMA-DDA approach for spheres and coated BC aggregates.

Main Methods:

• Systematic study of DDA discretization smoothing with EMA for boundary dipoles.
• Optical simulations of spheres and coated BC aggregates using EMA-DDA.
• Comparison with reference methods: Lorenz-Mie and multiple-sphere T-Matrix.

Main Results:

• EMA significantly improves DDA accuracy for spheres (up to 60x) and coated BC aggregates.
• EMA-DDA reduces simulation time by an order of magnitude for spheres.
• For coated BC, EMA improves accuracy, reducing extinction efficiency error from 4.7% to 0.3%.
• EMA-DDA achieves 1% accuracy with larger dipoles, resulting in ~30x faster simulations.

Conclusions:

• EMA effectively smooths DDA discretization, enhancing accuracy and efficiency.
• The EMA-DDA method is a powerful tool for simulating optical properties of complex particles.
• This approach offers substantial computational savings for accurate optical simulations.