Fast Calorimeter Simulation improvements for the ATLAS experiment

The full simulation of the ATLAS calorimeter using Geant4 is costly and will not be feasible due to the expected increase in data without the corresponding increase in CPU power. Instead, the parametrized fast simulation can be used, which can simulate particle showers faster and more efficiently. This report contains information about the validation of the fast calorimeter simulation against the full simulation and some modifications to the current fast calorimeter simulation code.