# The discrete dipole approximation for simulation of light scattering by particles much larger than the wavelength

## TL;DR

This paper evaluates the Discrete Dipole Approximation (DDA) for simulating light scattering by large particles, introduces an optimized parallel program, and compares results with exact Mie theory, highlighting computational challenges.

## Contribution

It presents an optimized, parallel DDA computer program capable of simulating large particles and compares its accuracy with exact solutions.

## Key findings

- Errors increase with refractive index m but not systematically with size parameter x.
- Computational times can exceed two weeks on 64 processors for large particles.
- The parallelization capability enables simulation of particles much larger than previously feasible.

## Abstract

In this manuscript we investigate the capabilities of the Discrete Dipole Approximation (DDA) to simulate scattering from particles that are much larger than the wavelength of the incident light, and describe an optimized publicly available DDA computer program that processes the large number of dipoles required for such simulations. Numerical simulations of light scattering by spheres with size parameters x up to 160 and 40 for refractive index m=1.05 and 2 respectively are presented and compared with exact results of the Mie theory. Errors of both integral and angle-resolved scattering quantities generally increase with m and show no systematic dependence on x. Computational times increase steeply with both x and m, reaching values of more than 2 weeks on a cluster of 64 processors. The main distinctive feature of the computer program is the ability to parallelize a single DDA simulation over a cluster of computers, which allows it to simulate light scattering by very large particles, like the ones that are considered in this manuscript. Current limitations and possible ways for improvement are discussed.

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Source: https://tomesphere.com/paper/0704.0037