  The discrete-dipole approximation (DDA) is a powerful method for calculating
absorption and scattering by targets that have sizes smaller than or comparable
to the wavelength of the incident radiation. We present a new prescription --
the Surface-Corrected Lattice Dispersion Relation (SCLDR) -- for assigning the
dipole polarizabilities that takes into account both target geometry and finite
wavelength. We test the SCLDR in DDA calculations using spherical and
ellipsoidal targets and show that for a fixed number of dipoles, the SCLDR
prescription results in increased accuracy in the calculated cross sections for
absorption and scattering. We discuss extension of the SCLDR prescription to
irregular targets.
