Method and system for lithographic simulation and verification

Methods and systems for lithographic simulation and verification comprising a process in the frequency domain or in the spatial domain of calculating intensity at a location (x, y) for a number of defocus values. In addition, evaluating the intensity calculation result to determine if the intensity level will result in the mask pattern being written onto a wafer. The verification process may be calculated in the spatial domain or in the frequency domain. The calculations may be done such that full focus window calculations may be obtained by isolating the defocus parameter "z" in the calculations.