In the DDSCAT+ user guide it is specified that the effective radius aeff = (3V/4*pi)1/3 where V is the volume represented by an array of N dipoles with lattice spacing d, then V = Nd3
For a rectangular prism of 17732 dipoles and dipole spacing of d = 0.5nm then, the volume is V = 2216.5 nm3. The effective radius would then be aeff = 8.088nm.
However, in actual use with a rectangular prism shaped array of 17732 dipoles and 0.5nm dipole spacing the effective radius given by the software is aeff = 32.353nm. This would be the effective radius were d = 2nm used for the spacing rather than d = 0.5nm as is specified in the same file as the given effective radius.
This is also true for the same shape with a dipole density of 3 per nanometer. The given dipole spacing and effective radius seem to not match up. Now the number of dipoles is N = 62040 and the file says d = 0.33nm but the given aeff = 73.674nm which would be true were d = 3nm.
It seems to me that the program uses a certain dipole spacing, but when calculating the effective radius it uses the reciprocal of that spacing. Am I incorrect, or missing something?