We present a theoretical methodology to study the electronic response properties of a chromophore physisorbed on a metal particle. In particular the chromophore is treated at ab initio level whereas the metal particle is described through its dielectric properties. The use of a boundary elements method for the resolution of the electrostatic problem allows the study of particles with complex shapes. The theoretical procedure is applied to the study of different quantities such as the chromophore effective polarizability, the UV-VIS absorption of the chromophore coated metal particle, and the surface enhanced Raman scattering (SERS) of the physisorbed molecule for two reliable chromophores (merocyanine dyes) physisorbed on copper and silver metal particles of various sizes and shapes. (C) 2001 American Institute of Physics.