Analytical expressions of the dispersive contributions of the nuclear   optical model
  Analytical solutions of dispersion relations in the nuclear optical model have been found for both imaginary volume and surface potentials. A standard Brown-Rho shape has been assumed for the volume imaginary term and a Brown-Rho shape multiplied by a decreasing exponential for the surface contribution. The analytical solutions are valid for any even value of the exponent appearing in these functional forms. 
J.M. Quesada, R. Capote, J. Raynal, A. Molina, M. Lozano