The new ATLAS Fast Calorimeter Simulation

With the huge amount of data collected with ATLAS, there is a need to produce a large number of simulated events. These productions are very CPU and time consuming when using the full GEANT4 simulation. FastCaloSim is a program to quickly simulate the ATLAS calorimeter response, based on a parameterization of the GEANT4 energy deposits of several kinds of particles in a grid of energy and eta. A new version of FastCaloSim is under development and its integration into the ATLAS simulation infrastructure is ongoing. The use of machine learning techniques improves the performance and decreases the memory usage. Dedicated parameterizations for the forward calorimeters are being studied. First results of the new FastCaloSim show substantial improvements of the description of energy and shower shape variables, including the variables for jet substructure.