Cautious note on using the discrete dipole approximation for inhomogeneous, spherical scatterers with high optical contrast

The discrete dipole approximation (DDA) is capable of treating scatterers with arbitrary shape and composition. However, large values of the refractive index require additional considerations. DDA calculations are performed for small spheres with a stronger absorbing inclusion and compared to T-matrix results. A natural phenomenon with strong optical contrasts is the melting of ice hydrometeors at microwave frequencies, and hence corresponding refractive indices are chosen. The obtained extinction and absorption efficiencies are found to depend mainly on the dipole size, whereas the phase function closely follows the T-matrix results by choosing a smaller stopping criterion and changing the polarizability formulation.