[en] A theoretical model is presented which predicts the output response of CCD to soft X-ray spectra. The model simulates the four fundamental parameters that ultimately limit CCD performance: Quantum efficiency, charge collection efficiency, charge transfer efficiency, and read noise. Simulated results are presented for a wide variety of CCD structures, and general conclusions are presented about achieving a practical balance of sensitivity, energy, and spatial resolution for an AXAF instrument. The authors compare the results of the analysis to an existing state-of-the-art CCD and project improvements which will be made in the near future