We compare the absorption of (a) an absorbing potential proposed recently by Manolopoulos based on semiclassical arguments and (b) complex potentials composed by contiguous square barriers. The latter use more parameters and provide better absorption, but the potential by Manolopoulos is simple and robust with respect to numerical discretization, and can be very efficient if its only effective parameter is optimized. (C) 2004 Elsevier B.V. All rights reserved.