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Abstract
The DDA Convert Tool takes a nonstandard geometry such as the model (left) and converts it to a collection of dipoles (right)
Dr. T. Wriedt
A common computational approach for studying the behavior of light (or generally electromagnetic radiation) is using Maxwell’s equations. These equations are well understood for a limited number of geometries (spheres, infinite cylinders, and others). For arbitrary structures, however, Maxwell’s Equations are insufficient. Another approach, DDA (discrete dipole approximation), can be used to compute the electromagnetic scattering of arbitrary, periodic, geometries. DDA discretizes an environment into a collection of dipoles, also called polarizable points. The interaction of light with each of these points, then, becomes a much simpler problem to understand and solve.
Nonstandard geometries are critical for optimizing nanobio systems
Myroshchenko et. al.
The DDSCAT software package provides an implementation of the DDA approach. We have provided a DDSCAT tool on NanoHub that provides a graphical interface as well as computational power to run your own DDA simulations. While the DDSCAT tool has a collection of fixed geometries which can be used to test the software, the arbitrary geometries must be provided by the user. These geometries can be created in common design applications such as “Blender” or any software which can generate a triangular mesh file. Before these files can be input into DDSCAT, however, they must be transformed into a collection of dipoles – which is the role of this tool, DDA Convert.
DDAConvert allows users to upload a triangular mesh surface and convert it to a volumebased dipole set that can be used by DDSCAT.
In order to create the dipole set, this algorithm first creates a cubic bounding box around the object, and scans every coordinate to see whether the point is inside or outside the object. For the points inside the object, a dipole is set at that position. This tool then outputs a file (shape.dat) which can then be used in DDSCAT. With this tool, nearly any particle shape can be used in DDSCAT simulations.
References
 R. Schuh, “Arbitrary particle shape modeling in DDSCAT and validation of simulation results,” in Proceedings of the DDAWorkshop, T. Wriedt and A. G. Hoekstra, Eds., pp. 22–24, Bremen, Germany (2007).
Cite this work
Researchers should cite this work as follows:

Draine, B.T., & Flatau, P.J. 1994, "Discrete dipole approximation for scattering calculations", J. Opt. Soc. Am. A, 11, 14911499
Draine, B.T., & Flatau, P.J. 2012, "User Guide to the Discrete Dipole Approximation Code DDSCAT 7.2"