Application of the extended boundary condition method to homogeneous particles with paint-group symmetries

The numerical evaluation of surface integrals is the most time-consuming pa rt of the extended boundary condition method (EBCM) for calculating the T m atrix. An efficient implementation of the method is presented for homogeneo us particles with discrete geometric symmetries and is applied to regular p olyhedral prisms of finite length. For such prisms, an efficient quadrature scheme for computing the surface integrals is developed. Exploitation of t hese symmetries in conjunction with the new quadrature scheme leads to a re duction in CPU time by 3 orders of magnitude from that of a general EBCM im plementation with no geometry-specific adaptations. The improved quadrature scheme and the exploitation of symmetries account for, respectively, 1 and 2 orders of magnitude in the total reduction of the CPU time. Test results for scattering by rectangular parallelepipeds and hexagonal plates are sho wn to agree well with corresponding results obtained by use of the discrete -dipole approximation. A model application for various polyhedral prisms is presented. (C) 2001 Optical Society of America.