Spherical and chromatic aberrations of electrostatic lenses with negative space charge in axial area are studied. A "toroidal subbeam" algorithm has been developed to model the evolution of the current and charge density distributions of intense charged particle beams taking into account space charge and initial thermal velocity effects. Optimized designs are presented which prove that negative spherical and chromatic aberration coefficients can be achieved for a space charge lens using an electron gun to produce the space charge cloud.